The Chicago Area Waterway System is a system of canals and channels with locks and dams in northeastern Illinois. The System links Lake Michigan with the Mississippi River. Although it has been a boon to commerce, tourism, transportation, and public health, it has created some problems. Two particular species of carp that could wreak monumental ecological damage to the Great Lakes have migrated up the Mississippi River and have entered the System. The Army Corps of Engineers and the Metropolitan Water Reclamation District of Greater Chicago have taken and are taking many steps to prevent the carp from reaching the Great Lakes. But the States of Michigan, Minnesota, Ohio, Pennsylvania, and Wisconsin filed suit under the federal common law of nuisance and § 702 of the Administrative Procedure Act, alleging that the Corps and the District are not taking sufficient steps to avert the potential crisis. Judge Dow (N.D. Ill.) denied the plaintiffs' motion for a preliminary injunction. The States appeal.

In their opinion, Seventh Circuit Judges Manion, Wood, and Williams affirmed. The Court first stated the familiar elements needed for a preliminary injunction: likely to succeed on the merits, likely to suffer irreparable harm, the harm without an injunction is greater than the harm an injunction would impose on the defendants, and the injunction is in the public interest. The Court first addressed likelihood of success and expressed its disagreement with the district court's assessment of that as "modest." The Court concluded that the federal common law of nuisance applied to the State's allegations, rejecting defendants' arguments that it did not apply because either the defendants were not physically moving the fish themselves or that the allegations did not involve a traditional pollutant. The Court briefly addressed, without deciding, the underdeveloped argument that a federal common law of nuisance claim it does not stand against the United States. Although it found that excluding such claims would be consistent with the origins of the tort, it also questioned why the claim could not lie against the United States as an owner of a dam or other facility that might create a nuisance. In any event, given its ultimate conclusion, the Court proceeded on the assumption that the claim was appropriate. Next, the Court addressed the Corps' claim of sovereign immunity and concluded that APA § 702 waives sovereign immunity for these declaratory and injunctive claims. The Court moved to the defendants’ displacement doctrine argument. That doctrine addresses the relationship between the courts and Congress and provides that the exercise of federal common law by the courts in an area is no longer necessary once Congress addresses the question. The question presented here is whether Congress has done enough to displace the common law. In Milwaukee I, Supreme Court said that Congress had not displace the federal common law even though it had enacted several laws touching upon the subject matter. In Milwaukee II and American Electric Power, however, the Supreme Court held that more comprehensive legislation in the areas did displace the federal common law. Here, although the Court recognized some Congressional activity (for example, the National Invasive Species Act) in the area, it concluded that it fell far short of the comprehensive schemes in Milwaukee II and American Electric Power and did not displace the federal common law. The Court turned to the actual evidence presented by the plaintiffs on their claim and considered whether the identified activity was a nuisance and whether it was sufficiently threatening to require equitable relief. Although the Court found little error in the district court's factual findings that the potential for harm was significant, it disagreed with its conclusion that the risk of that harm occurring was not sufficient to warrant injunctive relief. The Court noted that the magnitude of the potential harm was tremendous, that it was increasing, and that it probably could not be undone if once it occurred. It therefore gave the benefit of the doubt to the plaintiffs that the risk was imminent and concluded that they satisfied the likelihood of success element needed for a preliminary injunction. With respect to plaintiffs' likelihood of success on its APA claim, the Court concluded that that claim was co-extensive with the federal common law claim and need not be addressed separately. The second element required for a preliminary injunction is irreparable harm. The Court concluded that plaintiffs met their burden of showing irreparable harm, relying on much the same evidence relevant to the likelihood of success element. Again, it concluded (as, apparently, did the parties) that the harm, if it occurred, would be genuinely irreparable. And again, given the severity of that harm, it gave the States the benefit of the doubt on the degree of risk that the harm would actually occur. The Court turned to the balancing of harms -- comparing the harm that would occur in the absence of an injunction with the harm an injunction would impose on the defendants. It concluded that the harm to the defendants in the event the injunction issued substantially outweighed any benefit to the plaintiffs for two reasons. First, it evaluated the specific requests for relief individually and found substantial problems inherent in the requests. Some of the requests provided little benefit at significant cost. At least one of the request was already under study by the Corps. Simply put, the record did not establish that the requested relief would do much to address the problem and, to the extent it would, it created other risks. It compared that "benefit" with the harm an injunction would impose on the defendants. It concluded that it would impose significant cost, it would increase the risk of flooding, it would negatively impact commercial and recreational boating, and it would interfere with police and fire protection services on the Chicago River. Second, the Court concluded that an injunction would interfere with the ongoing efforts of the federal and local agencies already addressing the problem. Federal courts, it said, should tread carefully when federal and state agencies, expert in the area, are already addressing a problem. In concluding that the district court did not abuse its discretion in denying injunctive relief, the Court emphasized that the landscape could change at any time. New evidence is being developed on an almost daily basis and the agency response is subject to political pressures and budgets. Any significant change in that landscape could be grounds for the district court's re-examination of the issue.