NATURAL RESOURCES DEFENSE COUNCIL, Northwest Environmental Advocates, Center for Biological Diversity, and National Wildlife Federation v. UNITED STATES ENVIRONMENTAL PROTECTION AGENCY, Lake Carriers' Association and Canadian Shipowners Association, Intervenors

CHIN, Circuit Judge: This case arises from the efforts of the Environmental Protection Agency (“EPA”) pursuant to section 402(a) of the Clean Water Act (the “CWA”), 33 U.S.C. § 1342(a), to regulate the discharge of ballast water from ships.1 A ship takes on and discharges ballast water to compensate for changes in its weight caused by activities such as loading and unloading cargo or consuming fu