Here is the opinion.

An excerpt:

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’ commonlaw 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.