Full opinion text
WOOD, Circuit Judge. Ambitious engineering projects that began at the time that the City of Chicago was founded have established a waterway in northeastern Illinois that connects Lake Michigan to the Mississippi watershed. (Additional links between the Mississippi and the Great Lakes exist elsewhere, from northern Minnesota to New York.) The system of canals, channels, locks, and dams, with which we are concerned, known today as the Chicago Area Waterway System (or CAWS, as the parties call it in their briefs), winds from the mouth of the Chicago River and four other points on Lake Michigan to tributaries of the Mississippi River in Illinois. The navigable link has been a boon to industry and commerce, and it supports transportation and recreation. Public health crises that once were common because the Chicago River emptied the City’s sewage into the lake— the City’s freshwater supply — vanished thanks to the Chicago Sanitary and Ship Canal, which reversed the flow of the Chicago River so that it now pulls water from the lake, into the CAWS, and down toward the Mississippi. During heavy rains and seasonal high waters in the region, the CAWS is used to control flooding. This effort to connect the Great Lakes and Mississippi watersheds has not been without controversy. At the turn of the 20th century, Missouri sued in the Supreme Court to stop Illinois from opening the Sanitary and Ship Canal. An opinion by Justice Holmes rejected Missouri’s challenge; the Court concluded that the state had not presented enough evidence to establish that the flow of sewage toward the Mississippi would create a public nuisance. Missouri v. Illinois, 200 U.S. 496, 26 S.Ct. 268, 50 L.Ed. 572 (1906); see also Missouri v. Illinois, 180 U.S. 208, 21 S.Ct. 331, 45 L.Ed. 497 (1901). Several years later a broader fight erupted among the states bordering the Great Lakes, and the Court began to issue decrees setting the maximum rate at which Illinois may divert water away from Lake Michigan and into the CAWS. E.g., Wisconsin v. Illinois, 449 U.S. 48, 101 S.Ct. 557, 66 L.Ed.2d 253 (1980); Wisconsin v. Illinois, 388 U.S. 426, 87 S.Ct. 1774, 18 L.Ed.2d 1290 (1967); Wisconsin v. Illinois, 311 U.S. 107, 61 S.Ct. 154, 85 L.Ed. 73 (1940); Wisconsin v. Illinois, 278 U.S. 367, 49 S.Ct. 163, 73 L.Ed. 426 (1929). Nor has opening a pathway between these bodies of fresh water come without costs. This appeal requires us to consider one of those costs: the environmental and economic harm posed by two invasive species of carp, commonly known as Asian carp, which have migrated up the Mississippi River and now are poised at the brink of this man-made path to the Great Lakes. The carp are voracious eaters that consume small organisms on which the entire food chain relies; they crowd out native species as they enter new environments; they reproduce at a high rate; they travel quickly and adapt readily; and they have a dangerous habit of jumping out of the water and harming people and property. In an attempt to stop the fish, Michigan, Minnesota, Ohio, Pennsylvania, and Wisconsin, all states bordering the Great Lakes, filed this lawsuit against the U.S. Army Corps of Engineers (the Corps) and the Metropolitan Water Reclamation District of Greater Chicago (the District), which together own and operate the facilities that make up the CAWS. The plaintiff states allege that the Corps and the District are managing the CAWS in a manner that will allow invasive carp to move for the first time into the Great Lakes. The states fear that if the fish establish a sustainable population there, ecological disaster and the collapse of billion-dollar industries that depend on the existing ecosystem will follow. They say that the defendants’ failure to close down parts of the CAWS to avert the crisis creates a grave risk of harm, in violation of the federal common law of public nuisance, see American Electric Power Co., Inc. v. Connecticut, — U.S. -, 131 S.Ct. 2527, 180 L.Ed.2d 435 (2011), and they advance a related claim against the Corps based on the Administrative Procedure Act (APA), 5 U.S.C. § 702. The states asked the district court for declaratory and injunctive relief and moved for a preliminary injunction that would require the defendants to put in place additional physical barriers throughout the CAWS, implement new procedures to stop invasive carp, and expedite a study of how best to separate the Mississippi and Great Lakes watersheds permanently. Other parties intervened to protect their interests — the Grand Traverse Band of Ottawa and Chippewa Indians on the side of the plaintiffs, and the City of Chicago, Wendella Sightseeing Company, and the Coalition to Save Our Waterways as defendants. The district court denied the motion for a preliminary injunction, and the states appealed immediately. See 28 U.S.C. § 1292(a)(1). We conclude that the court’s decision to deny preliminary relief was not an abuse of discretion. Our analysis, however, differs in significant respects from that of the district court, which was persuaded that the plaintiffs had shown only a minimal chance of succeeding on their claims. We are less sanguine about the prospects of keeping the carp at bay. In our view, the plaintiffs presented enough evidence at this preliminary stage of the case to establish a good or perhaps even a substantial likelihood of harm — that is, a non-trivial chance that the carp will invade Lake Michigan in numbers great enough to constitute a public nuisance. If the invasion comes to pass, there is little doubt that the harm to the plaintiff states would be irreparable. That does not mean, however, that they are automatically entitled to injunctive relief. The defendants, in collaboration with a great number of agencies and experts from the state and federal governments, have mounted a full-scale effort to stop the carp from reaching the Great Lakes, and this group has promised that additional steps will be taken in the near future. This effort diminishes any role that equitable relief would otherwise play. Although this case does not involve the same kind of formal legal regime that caused the Supreme Court to find displacement of the courts’ common-law powers in American Electric Power, on the present state of the record we have something close to it. In light of the active regulatory efforts that are ongoing, we conclude that an interim injunction would only get in the way. We stress, however, that if the agencies slip into somnolence or if the record reveals new information at the permanent injunction stage, this conclusion can be revisited. I To justify a preliminary injunction, the plaintiff states must show that they are likely to succeed on the merits of their claims, that they are likely to suffer irreparable harm without an injunction, that the harm they would suffer without the injunction is greater than the harm that preliminary relief would inflict on the defendants, and that the injunction is in the public interest. Winter v. Natural Res. Def. Council, Inc., 555 U.S. 7, 20, 129 S.Ct. 365, 172 L.Ed.2d 249 (2008). We will affirm the decision to deny a preliminary injunction unless the district court has abused its discretion. Judge v. Quinn, 612 F.3d 537, 557 (7th Cir.2010). As usual, we review questions of fact for clear error and questions of law de novo. Girl Scouts of Manitou Council, Inc. v. Girl Scouts of United States of Am., Inc., 549 F.3d 1079, 1086-87 (7th Cir.2008). II We begin with the states’ likelihood of succeeding on their common law public nuisance claim. The district court thought that the states had “at best, a very modest likelihood of success.” For the reasons discussed below, we think that the district court underestimated the likely merit of the states’ claim, particularly at this early stage of the case. A The Supreme Court recently reminded us that when it said, “There is no federal general common law,” in Erie Railroad Co. v. Tompkins, 304 U.S. 64, 78, 58 S.Ct. 817, 82 L.Ed. 1188 (1938), it did not close the door on federal common law entirely. American Electric Power, 131 S.Ct. at 2535-37. Instead, following Erie, a “keener understanding” of federal common law developed, under which federal courts “fill in ‘statutory interstices,’ and, if necessary, even ‘fashion federal law’ ” in areas “ ‘within national legislative power.’ ” Id. at 2535 (quoting Henry J. Friendly, In Praise of Erie — And of the New Federal Common Law, 39 N.Y.U. L.Rev. 383 (1964)). In American Electric Power, the Court reaffirmed a long line of cases that have “approved federal common law suits brought by one State to abate pollution emanating from another State.” 131 S.Ct. at 2535-36. These decisions reach at least as far back as the battle between Missouri and Illinois over sewage, see Missouri v. Illinois, supra, and they have continued from there, see Georgia v. Tennessee Copper Co., 206 U.S. 230, 27 S.Ct. 618, 51 L.Ed. 1038 (1907), New York v. New Jersey, 256 U.S. 296, 41 S.Ct. 492, 65 L.Ed. 937 (1921), New Jersey v. City of New York, 283 U.S. 473, 51 S.Ct. 519, 75 L.Ed. 1176 (1931), Illinois v. City of Milwaukee, 406 U.S. 91, 92 S.Ct. 1385, 31 L.Ed.2d 712 (1972) (Milwaukee I), City of Milwaukee v. Illinois, 451 U.S. 304, 101 S.Ct. 1784, 68 L.Ed.2d 114 (1981) (Milwaukee II), and American Electric Power, 131 S.Ct. 2527. But it has been recognized for a much longer period that the equitable power of the courts extends to suits to abate public nuisances. See United Steelworkers of America v. United States, 361 U.S. 39, 60-61, 80 S.Ct. 1, 4 L.Ed.2d 12 (1959) (Frankfurter, J., concurring) (assembling examples from 16th century England to the turn of the 20th century in the United States). It is our federal system that creates the need for a federal common law to govern interstate disputes over nuisances. Tennessee Copper explains that when the states joined the union and in so doing abandoned their right to abate foreign nuisances by force, “they did not thereby agree to submit to whatever might be done. They did not renounce the possibility of making reasonable demands on the ground of their still remaining quasi-sovereign interests; and the alternative to force is a suit in this court.” 206 U.S. at 237, 27 S.Ct. 618. A state that wants to bring a lawsuit attacking a nuisance emanating from outside of its borders faces at least two legal difficulties: whom to sue, and what law to apply? If the offender is another state, then the Constitution permits an original action in the Supreme Court. U.S. Const, art. Ill sec. 2, cl. 5. Whatever the venue, applicable law is a problem: the offending state owes no allegiance to the law of the plaintiff state, but the plaintiff state may rightly fear protectionism if the law of the offending state is used. Committee for Consideration of the Jones Falls Sewage Sys. v. Train, 539 F.2d 1006, 1008 (4th Cir.1976) (en banc). Responding to this concern, the Court has concluded that in the context of interstate nuisances “where there is an overriding federal interest in the need for a uniform rule of decision or where the controversy touches basic interests of federalism,” federal common law governs. Milwaukee I, 406 U.S. at 105 n. 6, 92 S.Ct. 1385. When evaluating claims based on the federal common law of nuisance, courts must be mindful that they do not have “creative power akin to that vested in Congress.” American Electric Power, 131 S.Ct. at 2536. 1 The states’ public nuisance action here is based on allegations that non-native species of carp (specifically, bighead and silver carp) will migrate through waterworks operated by the defendants from rivers connected to the Mississippi into Lake Michigan and on to the other Great Lakes. “When we deal with air and water in their ambient and interstate aspects, there is a federal common law.” Milwaukee I, 406 U.S. at 103, 92 S.Ct. 1385. We know that this body of law applies in a dispute about “the pollution of a body of water such as Lake Michigan bounded, as it is, by four States,” id. at 105 n. 6, 92 S.Ct. 1385. But the Court has cautioned that it has never “held that a State may sue to abate any and all manner of pollution originating outside its borders.” American Electric Power, 131 S.Ct. at 2536. The Corps and the District contend that the common law does not extend to the allegations in this case. They stress that they are not emitting “traditional pollutants”; all they have done, they say, is to operate facilities in the CAWS through which invasive species already living in local rivers might travel on their own. We can dismiss the latter part of this argument without much discussion: the defendants bear responsibility for nuisances caused by their operation of a manmade waterway between the Great Lakes and Mississippi watersheds. That they are not themselves physically moving fish from one body of water to the other does not mean that their normal operation of the CAWS cannot cause a nuisance. See, e.g., Restatement (Second) Torts § 834 (“One is subject to liability for a nuisance caused by an activity, not only when he carries on the activity but also when he participates to a substantial extent in carrying it on.”) & cmt. (b) (defining “activity” to include acts “that create physical conditions that are harmful to neighboring land after the activity that created them has ceased”). Similarly, we know of no rule saying that the defendants must emit a “traditional pollutant” in order for federal common law to apply. While it may be true that the introduction of an invasive species of fish into a new ecosystem does not fit the concept of nuisance as neatly as a spill of toxic chemicals into a stream, we do not think the Supreme Court has limited the concept of public nuisance as much as the defendants suggest. A public nuisance is defined as a substantial and unreasonable interference with a right common to the general public, usually affecting the public health, safety, peace, comfort, or convenience. Restatement (Second) Torts § 821B; Dan B. Dobbs, the Law op Torts § 467, at 1334 (2000). It would be arbitrary to conclude that this type of action extends to the harm caused by industrial pollution but not to the environmental and economic destruction caused by the introduction of an invasive, non-native organism into a new ecosystem (assuming that the states have correctly forecast the depletion of the Great Lakes fishery and the corresponding damage to the multi-billion-dollar sports fishing industry). Public nuisance traditionally has been understood to cover a tremendous range of subjects: It includes interferences with the public health, as in the case of a hogpen, the keeping of diseased animals, or a malarial pond; with the public safety, as in the case of the storage of explosives, the shooting of fireworks in the streets, harboring a vicious dog, or the practice of medicine by one not qualified; with public morals, as in the case of houses of prostitution, illegal liquor establishments, gambling houses, indecent exhibitions, bullfights, unlicensed prize fights, or public profanity; with the public peace, as by loud and disturbing noises, or an opera performance which threatens to cause a riot; with the public comfort, as in the case of bad odors, smoke, dust and vibration; with public convenience, as by obstructing a highway or a navigable stream, or creating a condition which makes travel unsafe or highly disagreeable, or the collection of an inconvenient crowd; and in addition, such unclassified offenses as eavesdropping on a jury, or being a common scold. Keeton, et al, Prosser and Keeton on Torts § 90, at 643-45 (5th ed.1984) (citations omitted). The Supreme Court’s application of public nuisance principles to cases involving shared water resources reflects this broad understanding. For example, the Court has held that a change in one state’s water-drainage system that causes flooding on another state’s farms may create a public nuisance, see North Dakota v. Minnesota, 263 U.S. 365, 374, 44 S.Ct. 138, 68 L.Ed. 342 (1923); just as the industrial contamination of a body of water might, Arizona Copper Co. v. Gillespie, 230 U.S. 46, 57, 33 S.Ct. 1004, 57 L.Ed. 1384 (1913). In this vein, American Electric Power emphasized “that public nuisance law, like common law generally, adapts to changing scientific and factual circumstances.” 131 S.Ct. at 2536. The types of invasive carp that are the concern in this case have been designated as injurious species by the U.S. Fish and Wildlife Service, see 50 C.F.R. § 16.13(a)(2)(v); this designation means that it is a federal crime under the Lacy Act to transport them around or into the United States, 16 U.S.C. §§ 3371-78. We conclude that the federal common law of public nuisance extends to the problem that the plaintiff states have identified. The next question, which is raised only by the Corps, is whether the plaintiff states may state a claim based on the federal common law of public nuisance against the United States. The Corps asserts that “the States have shown no basis for recognizing a federal common-law public nuisance claim against a federal agency.” But the Corps has not developed the argument much beyond this broad statement. Its brief moves instead to a discussion of whether federal common law has been displaced by congressional legislation and whether there is any role for the courts to play when agencies have taken concerted action to address a problem. These are two important issues that we will explore below, but neither point explains why a claim based on the federal common law of public nuisance cannot move forward against the United States. The plaintiff states have done little to counter the Corps’s suggestion. They reply (unresponsively, in our view) that “the federal common law of public nuisance undoubtedly exists.” The implications of finding that the United States has created a public nuisance strike us as potentially important and complex; this is not a topic that can be thrown on the table and then ignored. In this connection, it is telling that the Supreme Court went out of its way in American Electric Power to point out that it “ha[d] not yet decided whether private citizens ... or political subdivisions ... of a State may invoke the federal common law of nuisance to abate out-of-state pollution.” 131 S.Ct. at 2536. It declined to answer that question because it thought it best to resolve the case on other grounds. But the Court’s statement cautions us to tread carefully whenever we consider how far to push a theory of federal common law. This concern is less pressing for claims the Court has already recognized, such as those against state or local governmental entities or private parties. See, e.g., Missouri v. Illinois, 200 U.S. 496, 26 S.Ct. 268 (states), Milwaukee I, 406 U.S. 91, 92 S.Ct. 1385 (political subdivisions); Tennessee Copper, 206 U.S. 230, 27 S.Ct. 618 (private citizens). We have not discovered any case in which the Supreme Court has expressly authorized a public nuisance action against the United States in its sovereign capacity. A recent concurring opinion in the D.C. Circuit makes the same observation, noting that “the Court has not endorsed any federal common-law causes of action against the Government during the post-Erie period.” Et-Shifa Pharm. Indus. Co. v. United States, 607 F.3d 836, 853 (D.C.Cir.2010) (Kavanaugh, J., concurring). To understand common-law public nuisance in a way that would exclude suits against the United States would be faithful to the ancient origins of nuisance, where the term described the criminal act of infringing on the rights of the Crown, see William L. Prosser, Private Action for Public Nuisance, 52 Va. L.Rev. 997, 998 (1966); at least during that era, no one would have contemplated that the King or Queen could be the source of a nuisance. Whether this sort of sovereign prerogative has any place in modern American law, as a concept distinct from the sovereign immunity of the United States, is a separate question. Perhaps there is also a modern justification for the position that the federal common law of public nuisance cannot operate against the government: this area of federal common law exists to provide a uniform rule for interstate disputes that will serve the national interest, and it may be thought illogical to say that a federal actor, which in theory embodies the national interest, is at the same time violating a judge-made concept of that same interest. On the other hand, there are respectable arguments in favor of applying public nuisance to the acts of federal agencies, depending on the activity in which the agency is engaged. We have moved far beyond the Divine Right of Kings and the concept that the Crown can do no wrong. We may assume that an agency’s effort to regulate private actors in a particular area would not give rise to a claim of public nuisance. But it is hard to see why the United States’s ownership of a dam, power plant, or other facility should automatically foreclose a public nuisance claim brought by a state for harms created by the operation of that facility. If the facility were located in and owned by State A and it was damaging State B, then State B would be entitled to assert a common-law claim against State A (or one of its subdivisions or private citizens). Our case offers a good illustration of the point: the Corps and the District together operate facilities that are allegedly on the verge of creating a nuisance in waters of the plaintiff states; why should the plaintiffs be able to state a claim against the District but not the Corps? The possible inconsistencies that would be created by such a rule may be the reason that no court has expressed concern about the appearance of the Tennessee Valley Authority — a federally owned entity that was created by Congress and acts like a private corporation — as a defendant in a public nuisance lawsuit. See American Electric Power, 131 S.Ct. 2527; North Carolina ex rel. Cooper v. TVA, 615 F.3d 291 (4th Cir.2010); North Carolina ex rel. Cooper v. TVA, 515 F.3d 344 (4th Cir.2008). In fact, out of all public nuisance decisions we have identified from either the Supreme Court or the Courts of Appeals that involve a federal agency as a defendant, none contains a whisper of discussion about whether the claim runs against the United States. In addition to the cases just mentioned, see Middlesex Cnty. Sewerage Auth. v. National Sea Clammers Ass’n, 453 U.S. 1, 4 & n. 3, 101 S.Ct. 2615, 69 L.Ed.2d 435 (1981) (claims against the Environmental Protection Agency (EPA) and the Corps); Committee for Consideration of Jones Falls Sewage Sys., 539 F.2d 1006 (claims against the EPA); Massachusetts v. U.S. Veterans Admin., 541 F.2d 119 (1st Cir.1976) (claims against the Veterans Administration). Whether the plaintiffs’ common-law action can proceed against the Corps is a question that may well require attention as this case proceeds. Given the parties’ cursory exposition of the issue and our ultimate conclusion that preliminary relief is not warranted, we find it unnecessary to say more at this point. (We see this as a question relating to the plaintiffs’ ability to state a claim; it does not implicate the court’s jurisdiction, and so there is nothing to prevent our declining to reach it.) For now, we will assume that the states’ federal common-law claim may proceed against all of the defendants. B The defendants argue that two additional obstacles also diminish the states’ likelihood of succeeding on their public nuisance claim. The first concerns the sovereign immunity of the United States. The Corps contends that even if it makes sense to apply public nuisance principles against the United States, the Corps is nevertheless not subject to suit because the United States has not waived its sovereign immunity for this kind of claim. The second argument, which we address below, is that congressional regulation of the invasive carp problem has displaced any role for federal common law. “Absent a waiver, sovereign immunity shields the Federal Government and its agencies from suit.” F.D.I.C. v. Meyer, 510 U.S. 471, 475, 114 S.Ct. 996, 127 L.Ed.2d 308 (1994). The Corps takes the position that there is no such waiver of immunity for lawsuits against the United States that seek declaratory and injunctive relief based on a federal common-law tort. Whether this is correct depends on the interaction between section 702 of the APA and the Federal Tort Claims Act (FTCA), 28 U.S.C. § 1346(b). We begin with a look at the APA. Section 702 reads as follows: A person suffering legal wrong because of agency action, or adversely affected or aggrieved by agency action within the meaning of a relevant statute, is entitled to judicial review thereof. An action in a court of the United States seeking relief other than money damages and stating a claim that an agency or an officer or employee thereof acted or failed to act in an official capacity or under color of legal authority shall not be dismissed nor relief therein be denied on the ground that it is against the United States or that the United States is an indispensable party. 5 U.S.C. § 702. “The first and second sentences of § 702 play quite different roles.” Veterans for Common Sense v. Shinseki, 644 F.3d 845, 866 (9th Cir.2011). The first supplies a right to seek review of agency action; the second, added by the 1976 amendments to the statute, provides a waiver of sovereign immunity. Id. The waiver covers actions that seek specific relief other than money damages; this aptly describes the plaintiffs’ claim for declaratory and injunctive relief. See Blagojevich v. Gates, 519 F.3d 370, 371-72 (7th Cir.2008) (noting that § 702 “waived sovereign immunity for most forms of prospective relief’); see also Bowen v. Massachusetts, 487 U.S. 879, 893,108 S.Ct. 2722,101 L.Ed.2d 749 (1988) (construing § 702’s waiver broadly and remarking that “complaints [for] declaratory and injunctive relief ... [are] certainly not actions for money damages”); Veterans for Common Sense, 644 F.3d at 864-65. Moreover, the waiver in § 702 is not limited to claims brought pursuant to the review provisions contained in the APA itself. The waiver applies when any federal statute authorizes review of agency action, as well as in cases involving constitutional challenges and other claims arising under federal law. Blagojevich, 519 F.3d at 372; Czerkies v. U.S. Dep’t of Labor, 73 F.3d 1435, 1437-38 (7th Cir.1996) (en banc); see also Veterans for Common Sense, 644 F.3d at 867-68; Trudeau v. Federal Trade Comm’n, 456 F.3d 178, 186-87 (D.C.Cir.2006); United States v. City of Detroit, 329 F.3d 515, 520-21 (6th Cir.2003) (en banc); Jajfee v. United States, 592 F.2d 712, 718 (3d Cir.1979). Although the United States has argued from time to time that the “final agency action” requirement of § 704 limits the waiver of immunity in § 702, it has not prevailed on that ground. E.g., Veterans for Common Sense, 644 F.3d at 866-68; Trudeau, 456 F.3d at 186-87. The Corps wisely does not take that position here; as the Ninth Circuit explained recently, the conditions of § 704 affect the right of action contained in the first sentence of § 702, but they do not limit the waiver of immunity in § 702’s second sentence. Veterans for Common Sense, 644 F.3d at 866-68. The only limitation on § 702 that requires our attention is the clause that says, “Nothing herein ... confers authority to grant relief if any other statute that grants consent to suit expressly or impliedly forbids the relief which is sought,” 5 U.S.C. § 702(2), which Congress added to the statute at the same time that it introduced the waiver of sovereign immunity, see Pub.L. 94-574, 90 Stat. 2721 (Oct. 21, 1976). Pointing to this provision, the Corps frames an argument by negative implication: it says that when Congress enacted the FTCA in 1946, it did so against a backdrop of no tort liability for the United States; the FTCA waives the government’s sovereign immunity in suits for money damages to the extent that a private person would be held liable under applicable state tort law, see 28 U.S.C. § 1346(b)(1); Smith v. United States, 507 U.S. 197, 201-02, 113 S.Ct. 1178, 122 L.Ed.2d 548 (1993); Parrott v. United States, 536 F.3d 629, 635 (7th Cir.2008); but while the FTCA authorizes actions for damages, it says nothing at all about injunctive relief; thus, the FTCA implicitly prohibits injunctive relief in tort suits against the United States; and because of § 702(2), the Corps’s argument concludes, the plaintiffs cannot use the APA’s waiver of immunity to assert a common-law tort claim against the United States. That argument reads too much into congressional silence. The FTCA authorizes various tort claims for damages against the government to the extent that state law would provide relief, and it spells out a number of explicit exceptions. E.g., 28 U.S.C. § 2674 (barring punitive damages and interest before judgment); id. § 2680 (limiting the waiver, among other circumstances, where the alleged tort concerns the government’s enforcement of a statute or a discretionary function). There is nothing in the statute suggesting that Congress meant to forbid all actions that were not expressly authorized. To the contrary, section 702(2) requires evidence, in the form of either express language or fair implication, that Congress meant to forbid the relief that is sought. The Corps’s effort to transform silence into implicit prohibition would seriously undermine Congress’s effort in the APA to authorize specific relief against the United States. When Congress amended the APA in 1976 it gave every indication that it intended to provide specific relief for all nonstatutory claims against the government. See Trudeau, 456 F.3d at 186-87 (noting that all the reports from Congress “identified as the measure’s clear purpose elimination of the sovereign immunity defense in all equitable actions” and that “the Senate Report plainly indicated that Congress expected the waiver to apply to nonstatutory actions”) (internal quotation marks and alterations removed); Jaffee, 592 F.2d at 718-19 (outlining the reasons for the amendments to § 702, the concern that some executive departments were hiding behind their immunity, and concluding, “It was therefore precisely for equitable actions under section 1331 that Congress enacted the amendments to section 702”). The D.C. Circuit has read the Tucker Act, which it interprets as the exclusive remedy for contract claims against the government, to include an implicit prohibition against specific relief in contract actions against the United States and thus to prevent reliance on the APA’s waiver of immunity in such cases. Sharp v. Weinberger, 798 F.2d 1521, 1523-24 (D.C.Cir. 1986) (Scalia, J.). But the same court has since decided that, whatever the unspoken effect of the Tucker Act may be, the FTCA does not contain a comparable implicit ban against specific relief in tort cases against the government, and thus that plaintiffs in such cases may take advantage of the waiver in § 702 of the APA. U.S. Info. Agency v. Krc, 989 F.2d 1211, 1216 (D.C.Cir.1993). To the same effect, we recently explained that while “[t]he tort claims act doesn’t authorize equitable relief. ... [T]he Administrative Procedure Act does,” and we went on to say that a plaintiff asserting a tort claim against a federal agency could take advantage of the APA to obtain equitable relief. Robinson v. Sherrod, 631 F.3d 839, 841 (7th Cir.2011). If that were not reason enough to reject the Corps’s immunity defense, there is more. By its terms, the FTCA does not apply to any federal common-law tort claim, no matter what relief is sought. As the Corps itself points out, state tort law— not federal law — is the source of substantive liability under the FTCA. See Meyer, 510 U.S. at 478-79, 114 S.Ct. 996; Sobitan v. Glud, 589 F.3d 379, 388-89 (7th Cir. 2009); cf. Smith, 507 U.S. at 198, 113 S.Ct. 1178 (no FTCA claim for tort committed in Antarctica, a sovereignless entity not subject to either state law or the law of a foreign country). The states’ tort claim is based entirely on federal common law, and so the claim would not be cognizable under the FTCA in the first place. Meyer, 510 U.S. at 478, 114 S.Ct. 996. And if the FTCA could never apply to the type of claim advanced, then there is no reason to think that it implicitly forbids a particular type of relief for a claim outside its scope. For all these reasons, we conclude that the waiver contained in § 702 of the APA subjects the Corps to the plaintiffs’ common-law claims for declaratory and injunctive relief. C The Corps and the District next contend that congressional regulation has displaced as a matter of law the federal common law on which the states rely. The district court rejected this argument on the ground that Congress had not done enough about the threat of invasive carp to qualify for displacement of the federal common-law claim. The defendants say this was error. As they see things, it is enough that Congress has passed legislation to stop the carp and that federal and state agencies are hard at work to address the problem. Because the parties disagree, about the effect of American Electric Power and the way in which the displacement analysis should proceed, we begin with a few important principles. The doctrine of displacement rests on the premise that federal common law is subject to the paramount authority of Congress. New Jersey v. New York, 283 U.S. 336, 348, 51 S.Ct. 478, 75 L.Ed. 1104 (1931); see also American Electric Power, 131 S.Ct. at 2537 (“[I]t is primarily the office of Congress, not the federal courts, to prescribe national policy in areas of special federal interest.”). “ ‘[W]hen Congress addresses a question previously governed by a decision rested on federal common law ... the need for such an unusual exercise of law-making by federal courts disappears.’ ” American Electric Power, 131 S.Ct. at 2537 (quoting Milwaukee II, 451 U.S. at 314,101 S.Ct. 1784). Displacement focuses on the relation between Congress and the federal courts — it is not a doctrine that is concerned with the relation between the federal courts and the executive branch. This is a distinction often neglected by courts, as well as by the parties to this case. Whether federal courts can or should play a role in the face of comprehensive agency action is a critical issue, which we address below, but executive action or lack thereof does not affect the displacement analysis. See American Electric Power, 131 S.Ct. at 2538-39 (rejecting the argument that an agency must have taken action before common law is displaced and explaining that the EPA’s outright refusal to regulate emissions would not create a role for federal common law because “the delegation [of regulatory authority from Congress to the agency] is what displaces federal law”); Milwaukee II, 451 U.S. at 317-18, 324 n. 18, 101 S.Ct. 1784 (concluding that displacement had occurred because “Congress ... has occupied the field through the establishment of a comprehensive regulatory program supervised by an expert administrative agency,” regardless of how thoroughly the agency has implemented that program) (emphasis added). Congress’s decision to assign a particular problem to an executive agency or its description of an agency’s role in addressing a problem may be evidence of displacement, but the ebb and flow of agency action neither diminishes nor increases the role of federal common law. The important displacement question is whether Congress has provided a sufficient legislative solution to the particular interstate nuisance here to warrant a conclusion that this legislation has occupied the field to the exclusion of federal common law. We readily concede that Congress has not been mute on the subject of the carp, but that simply underscores the critical question: how much congressional action is enough? In their supplemental memoranda filed after American Electric Power was decided, the defendants seize upon the statement from the opinion that we quoted above — that “the delegation is what displaces federal law.” 131 S.Ct. at 2538. Their view is that all Congress must do to displace federal law is to indicate its intention to delegate a particular problem to an executive agency. They read American Electric Power as an enlargement of whatever displacement doctrine existed previously. But the defendants have taken the Court’s statement out of context. The Court in that passage was responding to an argument that an agency must have acted pursuant to its statutory power before federal common law is displaced. See id. at 2538-39. The Court explained that this was not the case and that it is congressional action, not executive action, that guides the displacement analysis. In so ruling the Court did not establish a new test based solely on Congress’s delegation of regulatory power; it simply pointed out that delegation is one type of congressional action that is evidence of displacement. “The test for whether congressional legislation excludes the declaration of federal common law,” the Court said, “is simply whether the statute ‘speak[s] directly to [the] question’ at issue.” Id. at 2587 (quoting Mobil Oil Corp. v. Higginbotham, 436 U.S. 618, 625, 98 S.Ct. 2010, 56 L.Ed.2d 581 (1978), and citing Milwaukee II, 451 U.S. at 315, 101 S.Ct. 1784, and County of Oneida v. Oneida Indian Nation of N.Y., 470 U.S. 226, 236-37, 105 S.Ct. 1245, 84 L.Ed.2d 169 (1985)). Importantly, while Congress must have spoken to the particular question at issue, it is not necessary for us to find the same manifest congressional purpose that we would require in an analysis of whether Congress has preempted state law. Id. at 2537. Earlier federal nuisance cases provide additional insight into the level of congressional action that is sufficient to displace federal common law. In Milwaukee I, where Illinois sued Milwaukee and other cities to stop them from dumping sewage into Lake Michigan, the Court decided that the federal common law of public nuisance had not been displaced, despite the fact that Congress had by that time “enacted numerous laws touching interstate waters.” 406 U.S. at 101-07, 92 S.Ct. 1385. Laws that touched on the issue at hand were not enough, and thus the common-law action could move forward. At the same time, however, the Court foreshadowed that federal legislation “may in time pre-empt the field of federal common law of nuisance.” Id. at 107, 92 S.Ct. 1385. Six months after Milwaukee I, Congress passed sweeping amendments to the Federal Water Pollution Control Act (FWPCA), and nine years after its first decision, the Court decided in Milwaukee II that those amendments displaced federal common law in the area. 451 U.S. at 317-18, 101 S.Ct. 1784. The Court viewed the amended statute as “a comprehensive regulatory program supervised by an expert administrative agency,” and it noted that under that regulatory program “[e]very point source discharge is prohibited unless covered by a permit.” Id. at 317-18, 101 S.Ct. 1784. This permitting requirement brought every potential interstate water polluter within Congress’s administrative scheme; any discharge had to be done with the permission of the EPA or a qualifying state agency; and there were enforcement options available when polluters failed to meet the conditions of permits that had been issued. See id. at 310-11,101 S.Ct. 1784. Most recently, American Electric Power held “that the Clean Air Act and the EPA actions it authorizes displace any federal common law right to seek abatement of carbon-dioxide emissions from fossil-fuel fired power plants.” 131 S.Ct. at 2537. The Court found it important that the Clean Air Act requires the EPA to identify and establish performance standards for all carbon-dioxide emitters; the statute also “provides multiple avenues for enforcement,” which include state agencies (operating under power delegated by EPA), the EPA itself, criminal proceedings against violators, and private enforcement in the event that the EPA or the states fail to regulate emissions. If the EPA has not acted, states and private parties may petition the agency for a rulemaking, after which parties have a right to review in federal court. Id. at 2537-38. The Court concluded with the observation that “[t]he Act itself thus provides a means to seek limits on emissions of carbon dioxide from domestic power plants — the same relief the plaintiffs seek by invoking federal common law. We see no room for a parallel track.” Id. at 2538. For better or for worse, congressional efforts to curb the migration of invasive species, and of invasive carp in particular, have yet to reach the level of detail one sees in the air or water pollution schemes. In 1990, Congress passed the Aquatic Nuisance Prevention and Control Act in an attempt to stop the spread of zebra mussels and other nuisance species. See 16 U.S.C. §§ 4701 et seq. That statute established the Aquatic Nuisance Species Task Force and gave it the job of studying invasive species and implementing a program “to prevent introduction and dispersal of aquatic nuisance species” in the United States. See id. § 4722. In 1996, the National Invasive Species Act amended the 1990 law and directed the Corps and the task force to “investigate and identify environmentally sound methods for preventing and reducing the dispersal of aquatic nuisance species between the Great Lakes [basin] and the Mississippi River [basin] through the Chicago River Ship and Sanitary Canal,” including any methods that could be incorporated in the normal operation of the CAWS. Id. § 4722(i)(3)(A). This mandate led to the construction of an underwater electric barrier in the Chicago Ship and Sanitary Canal. The barrier sits just upstream of the point where the CAWS empties into the Des Plaines River; it is designed to deter fish from moving in either direction through the canal. In 2003 the Corps, relying on the continuing authority given to the Secretary of the Army in 33 U.S.C. § 2309a, began construction of a second barrier next to the first. The barrier projects received an additional influx of cash from the District of Columbia Appropriations Act of 2005, Pub.L. 108-335, § 345, 118 Stat. 1352 (Oct. 18, 2004). In 2007, Congress passed the Water Resources Development Act, Pub.L. No. 110-114, § 3061(b)(1), 121 Stat. 1121 (Nov. 8, 2007), which allowed the Corps to upgrade its first barrier and officially authorized the construction of the already-in-progress second barrier. Finally, the Corps received more money to- complete a third barrier as part of the American Reinvestment and Recovery Act of 2009. Sections 3061(b) and (d) of the Water Resources Development Act of 2007, supra, instructed the Corps to undertake two studies: a short-term examination of how the electric barrier systems might more effectively stop invasive species (this is the Efficacy Study, which so far consists of four interim reports, see http://www.lrc. usace.army.mil/AsianCarp/efficacy.htm); and a long-term study of how the Mississippi and Great Lakes basins might be separated on a more permanent basis (this is the Great Lakes and Mississippi River Interbasin Study or “GLMRIS,” see http:// glmris.anl.gov). In an appropriations bill for fiscal year 2009, Congress provided that “the Secretary of the Army shall implement measures recommended in the efficacy study, or provided in interim reports, authorized under section 3061 of the Water Resources Development Act of 2007 ... with such modifications or emergency measures as the Secretary of the Army determines to be appropriate, to prevent aquatic nuisance species from bypassing the Chicago Sanitary and Ship Canal Dispersal Barrier Project referred to in that section and to prevent aquatic nuisance species from dispersing into the Great Lakes.” Energy and Water Development and Related Agencies Appropriations Act 2010, Pub.L. No. 111-85, § 126, 123 Stat. 2845, 2853 (Oct. 28, 2009). This authority — referred to informally as the Section 126 power — is set to expire on September 30, 2011. Department of Defense and Full-Year Continuing Appropriations Act 2011, Pub.L. No. 112-10, §§ 1101(a)(2), 1104, 1106, 125 Stat. 38, 103 (Apr. 15, 2011). Add to these measures the appropriation of funds so that the Corps can ensure proper operation of the CAWS, e.g., Pub.L. No. 98-63, 97 Stat. 301, 311 (July 30,1983); Pub.L. No. 97-88 § 107, 95 Stat. 1135, 1137 (Dee. 4, 1981); Pub.L. No. 79-525, 60 Stat. 634, 636 (July 24, 1946), and one has the whole of Congress’s efforts to stop invasive species from moving through the CAWS. Recent legislative proposals targeted at halting invasive carp have failed in both Houses. E.g., Close All Routes and Prevent Asian Carp Today Act of 2010 (CARP ACT), H.R. 4472, S. 2946. Although this legislation demonstrates that Congress is aware of the problem of invasive species generally, and carp in particular, it falls far short of the mark set by the Clean Air Act or the Federal Water Pollution Control Act. Congress has not passed any substantive statute that speaks directly to the interstate nuisance about which the states are complaining. Most of the laws that we have summarized appropriate funds to the Corps for routine maintenance of the CAWS or for the electric barrier project. Apart from requiring the construction of these barriers and giving the Secretary of the Army temporary power to implement various recommendations, Congress has ordered agencies (or, more commonly, informal task forces composed of various executive actors) only to study the invasive species problem and propose solutions. Beyond that, neither the Corps nor any other agency has been empowered actively to regulate the problem of invasive carp, and Congress has not required any agency to establish a single standard to deal with the problem or to take any other action. The narrow delegation that has taken place bears little resemblance to the regulatory power that the EPA wields under the Clean Air Act. Tellingly, Congress has not provided any enforcement mechanism or recourse for any entity or party negatively affected by the carp, and there is certainly no recourse to the courts under the minimal scheme that has been established. The district court was correct that the current state of congressional regulation is much closer to the situation examined in Milwaukee I — and perhaps even less extensive than that — than the regimes reviewed in Milwaukee II or American Electric Power. D With these important preliminary questions out of the way, we are at last ready to consider whether the plaintiff states have presented enough evidence in support of their nuisance claim to establish that they are likely to succeed on the merits. The district court thought that the states failed to demonstrate more than a minimal chance of success. Before this court, the states contend that the district court misunderstood the elements of public nuisance. They point to the district judge’s statement that the tort “contemplates an active — or, at least, an imminent — threat of injury” as evidence of that error. In their view, all they must show to win final relief in a trial on the merits is that there is a “significant threat” that the nuisance will occur. This is a distinction without a difference; the district court correctly understood the law of public nuisance. Nonetheless, for different reasons we think that the district judge may have underestimated the states’ likelihood of success. We will elaborate on this point after a brief review of the governing law. 1 The district court began with the definition of public nuisance found in the Restatement (Second) of Torts, which has been a common reference point for courts considering cases arising under federal common law. See Connecticut v. American Electric Power Co., Inc., 582 F.3d 309, 351 & n. 28 (2d Cir.2009), rev’d on other grounds, American Electric Power, 131 S.Ct. 2527 (explaining that “[t]he Restatement definition of public nuisance has ... been used in ... federal eases involving the federal common law of nuisance ... and the Restatement principles have served as the backbone of state nuisance law”). The Restatement provides that “[a] public nuisance is an unreasonable interference with a right common to the general public,” Restatement (Second) of Torts § 821B(1), and it goes on to explain that conduct meets this standard when it interferes significantly with the public health, safety, peace, comfort, or convenience, id. § 821B(2)(a). We described above the reasons why the federal common law of public nuisance is available to redress the type of harm that the states have alleged. And all sides agree that if invasive carp were to achieve a sustainable population in the Great Lakes, the environmental and economic impact would qualify as an unreasonable interference with a public right. As the district court noted, the Corps and other agencies have repeatedly and publicly acknowledged the seriousness of the problem. The Corps, for example, has said that invasive carp “have the potential to damage the Great Lakes and confluent large riverine ecosystems,” and that it regards “[t]he prevention of an inter-basin transfer of bighead and silver carp from the Illinois River to Lake Michigan [as] paramount in avoiding ecologic and economic disaster.” As a result, the central question on the merits of the states’ public nuisance claim will be whether the harm that the states have described is sufficiently close to occurring that the courts should order the defendants to take some new action that will be effective to abate the public nuisance. We stress at the outset an important point to which we will return: this question is one that will be resolved after a full trial on the merits, rather than at this preliminary stage of the case. A court may grant equitable relief to abate a public nuisance that is occurring or to stop a threatened nuisance from arising. See Tennessee Copper, 206 U.S. at 238-39, 27 S.Ct. 618 (requiring the plaintiff to show that a defendant’s actions “cause and threaten damage”). In Missouri v. Illinois, 200 U.S. at 518, 26 S.Ct. 268, the Court wrote that the threatened harm underlying the nuisance claim “must be shown to be real and immediate.” We have read the Court’s cases to say that “[t]he elements of a claim based on the federal common law of nuisance are simply that the defendant is carrying on an activity that is causing an injury or significant threat of injury to some cognizable interest of the complainant,” Illinois v. City of Milwaukee, 599 F.2d 151, 165 (7th Cir.1979), rev’d on other grounds, Milwaukee II, 451 U.S. 304,101 S.Ct. 1784. Additional statements about averting threatened nuisances appear in the Restatement, see Restatement (Second) Torts § 821B cmt. (i) (“[F]or damages to be awarded [in public nuisance cases] significant harm must have been actually incurred, while for an injunction harm need only be threatened and need not actually have been sustained at all.”); id. § 821F cmt. (b) (“[E]ither a public or a private nuisance may be enjoined because harm is threatened that would be significant if it occurred.”), and in other treatises, see, e.g., 5 J. Pomeroy, A Treatise on Equity Jurisprudence and Equitable Remedies, § 1937 (§ 523), at 4398 (2d ed.1919) (noting that while “a mere possibility of a future nuisance will not support an injunction,” relief will be warranted when “the risk of its happening is greater than a reasonable man would incur”). The plaintiffs believe that the district court’s “imminent threat” requirement is inconsistent with these principles, but we do not share that view. The district court reproduced verbatim the elements of the claim as we described them in Illinois v. City of Milwaukee, supra. Its discussion of “immediacy” did nothing more than flesh out the Court’s requirement of a “real and immediate” threat in public nuisance cases. There is no meaningful legal difference for purposes of the ultimate resolution of a public nuisance claim between a threatened nuisance that is “imminent” and one that is “immediate,” “significant,” “real,” an “unreasonable risk,” or anything similar. The job of a court considering the merits of a public nuisance claim is simply to determine whether the activity complained of is a nuisance and, if so, whether it is sufficiently close to occurring that equitable relief is necessary to prevent it from happening. 2 We part company with the district court when it comes to the assessment of the states’ likelihood of success on the merits. Here we think it critical to bear in mind the difference between preliminary or interim relief, on the one hand, and permanent relief, on the other. The principles that we just reviewed relate to the ultimate outcome of a public nuisance proceeding. This case has not yet reached that stage, and one consequence of its preliminary posture is that the states were not required to prove that they will ultimately win on the merits in order to secure preliminary relief. “The propriety of preliminary relief and resolution of the merits are of course significantly different issues.” Parents Involved in Cmty. Schs. v. Seattle Sch. Dist. No. 1, 551 U.S. 701, 721 n. 10, 127 S.Ct. 2738, 168 L.Ed.2d 508 (2007) (internal quotation marks omitted). This is the reason why findings made at the preliminary injunction stage do not bind the district court as the case progresses. Cf. Guaranty Bank v. Chubb Corp., 538 F.3d 587, 591 (7th Cir.2008). The most significant difference between the preliminary injunction phase and the merits phase is that a plaintiff in the former position needs only to show “a likelihood of success on the merits rather than actual success.” Amoco Prod. Co. v. Village of Gambell, 480 U.S. 531, 546 n. 12, 107 S.Ct. 1396, 94 L.Ed.2d 542 (1987); cf. Chathas v. Local 131 Int’l Bhd. of Elec. Workers, 233 F.3d 508, 513 (7th Cir.2000) (“A plaintiff cannot obtain a permanent injunction merely on a showing that he is likely to win when and if the merits are adjudicated.”). In some cases, it is necessary to expedite an ultimate decision, and so courts sometimes consolidate the preliminary injunction hearing with the trial on the merits. See Fed.R.Civ.P. 65(a)(2). But where such consolidation has not taken place — and it has not here — and the question is the propriety of preliminary relief, the Supreme Court has warned against “improperly equating] ‘likelihood of success’ with ‘success’.... ” University of Texas v. Camenisch, 451 U.S. 390, 394, 101 S.Ct. 1830, 68 L.Ed.2d 175 (1981); see also Meridian Mut. Ins. Co. v. Meridian Ins. Group, Inc., 128 F.3d 1111, 1119 (7th Cir.1997). This is in keeping with the often-repeated rule that the threshold for establishing likelihood of success is low. E.g., Cooper v. Salazar, 196 F.3d 809, 813 (7th Cir.1999); Brunswick Corp. v. Jones, 784 F.2d 271, 275 (7th Cir.1986). We are concerned that the district court here may have lost sight of this distinction. By applying directly the law of public nuisance, the judge seems to have required the plaintiff states actually to show that they were entitled to permanent injunctive relief during the preliminary injunction hearing. The court concluded its discussion of the threat posed by invasive carp, for example, by saying that the states “ha[d] not made a convincing case” that the fish had pushed into the CAWS in significant numbers; and it said that the plaintiffs had not “shown that the fish [are] anywhere near ... establishing a population in Lake Michigan.” Because the states had not yet shown that the threat of nuisance was great enough in the final analysis to warrant an injunction to abate it, the district court seems to have assumed that they had also failed to show enough to obtain preliminary relief. To demonstrate the requisite likelihood of success, however, the states needed only to present a claim plausible enough that (if the other preliminary injunction factors cut in their favor) the entry of a preliminary injunction would be an appropriate step. The preliminary injunction, after all, is often seen as a way to maintain the status quo until merits issues can be resolved at trial. By moving too quickly to the underlying merits, the district court required too much of the plaintiffs and, correspondingly, gave too little weight to the strength of their claim at this stage of the case. 3 We also question the inferences drawn by the district court from the facts that it so carefully found after evaluating five days of hearings, which included the testimony of expert witnesses and volumes of written materials on complex scientific and engineering issues. There is very little to criticize about the court’s factual findings themselves. For instance, the district judge’s decision to admit the expert testimony of Dr. David Lodge, who has been hired by the Corps and who testified for the states at the preliminary injunction hearing about his efforts to track invasive carp through the use of environmental DNA (eDNA) testing, reflects a proper application of Federal Rule of Evidence 702. (We agree that any lack of peer review of Dr. Lodge’s work would go to the weight of his testimony, not to the court’s ability to consider it. Moreover, the situation will be different at the merits phase, given Dr. Lodge’s recent publication of his research. See Christopher L. Jerde, Andrew R. Mahon, W. Lindsay Chadderton & David M. Lodge, “Sight Unseen ” Detection of Rare Aquatic Species Using Environmental DNA 4 Conservation Letters 150 (April/May 2011).) We also see nothing to criticize in the district court’s assessment that the electric barriers built by the Corps near the intersection of the Chicago Sanitary and Ship Canal and the Des Plaines River seem to have at least some deterrent effect on the movement of invasive carp toward the Great Lakes. In addition, we consider it significant, as the district judge did, that efforts to detect carp by techniques including netting, so-called electrofishing, and rotenone poisoning, have led to few signs of the carp. Along the same lines, the district court was right to take into account the results of eDNA testing. Despite its skepticism about the reliability of the technique and its concern that the state of eDNA science “did not permit a reasonable inference that live Asian carp are in the [CAWS] ... in numbers that present an imminent threat,” the court acknowledged that the eDNA evidence lent some support to the conclusion that there may be invasive carp above (ie., lakeside of) the Corps’s electric barriers. Although we are less skeptical of the science than the district court, we too believe that caution in drawing inferences from the existence of carp DNA in the water is warranted. The eDNA technique, which tests water samples for markers matching a particular species, has a number of shortcomings: it is difficult, if not impossible, to know definitively whether a positive result signals a living specimen above the barrier (DNA may be shed by a dead or distant fish); a positive test does not reveal the number of live fish; and negative results do not necessarily signal the absence of carp. Efforts to corroborate eDNA results with traditional methods of capturing fish have not been successful thus far. On the other hand, the evidence is worth something. The eDNA technique detects carp when the fish are present in small numbers and in situations where the other fishing methods we described above might scare them away or simply miss them, and the large number of negative test results make sense given the sensitivity of the technique. In addition, the Corps and other agencies have voted with their feet: they have been using eDNA tests to manage the invasive car