Dist. Ct. did not err in granting defendant-Corps of Engineers motion to dismiss for failure to state claim plaintiffs’ action under federal common law of public nuisance and Administrative Procedure Act seeking injunction to compel defendant to take additional steps to prevent Asian carp from crossing into Lake Michigan. Although it was legally possible for plaintiffs to bring public nuisance claim against fed. govt., plaintiffs failed to allege facts showing that defendant was operating Chicago Sanitary and Ship Canal in manner that was likely to allow Asian carp to migrate into Lake Michigan. Ct., though, did not adopt Dist. Ct.’s view that defendant was authorized to operate navigable waterway regardless of environmental cost or that any such authorization would relieve defendant of duty to try to stop spread of Asian carp.