Section 404(a) regulates the discharge of dredged or fill material into 'navigable waters.' The Corps (D) has interpreted §404(a) to confer federal authority over an abandoned sand and gravel pit in northern Illinois which provides habitat for migratory birds. Solid Waste (P) is a consortium of 23 suburban Chicago cities and villages that united in an effort to locate and develop a disposal site for baled nonhazardous solid waste. P really liked an old mining site. P purchased the site for disposal of their baled nonhazardous solid waste. P contacted D to determine if a federal landfill permit was required under §404(a) of the CWA, 33 U. S. C. §1344(a). D had authority to issue permits 'for the discharge of dredged or fill material into the navigable waters at specified disposal sites.' D has issued regulations defining the term 'waters of the United States' to include 'waters such as intrastate lakes, rivers, streams (including intermittent streams), mudflats, sandflats, wetlands, sloughs, prairie potholes, wet meadows, playa lakes, or natural ponds, the use, degradation or destruction of which could affect interstate or foreign commerce ... .' D initially concluded that it had no jurisdiction over the site because it contained no 'wetlands,' or areas which support 'vegetation typically adapted for life in saturated soil conditions.' The Illinois Nature Preserves Commission informed D that a number of migratory bird species had been observed at the site. D asserted jurisdiction over the balefill site pursuant to subpart (b) of the 'Migratory Bird Rule.' D found the waters on the site to qualify as `waters of the United States' ... based upon the following criteria: (1) the proposed site had been abandoned as a gravel mining operation; (2) the water areas and spoil piles had developed a natural character; and (3) the water areas are used as habitat by migratory bird [sic] which cross state lines.' D refused to issue a §404(a) permit. P sued under the Administrative Procedure Act, 5 U. S. C. §701. The District Court granted summary judgment to D on the jurisdictional issue. At the Court of Appeals for the Seventh Circuit, P attacked D's assertion of jurisdiction over the site in that D had exceeded their statutory authority in interpreting the CWA to cover nonnavigable, isolated, intrastate waters based upon the presence of migratory birds and, in the alternative, that Congress lacked the power under the Commerce Clause to grant such regulatory jurisdiction. The Circuit held for D on 'the cumulative impact doctrine, under which a single activity that itself has no discernible effect on interstate commerce may still be regulated if the aggregate effect of that class of activity has a substantial impact on interstate commerce.' The Supreme Court granted certiorari.