The Clean Water Act (CWA) aims to 'restore and maintain the chemical, physical, and biological integrity of the Nation's waters.' The CWA divides the authority to issue permits to discharge pollutants between the United States Environmental Protection Agency and D, conferring on the latter the power to issue permits for discharges of 'dredged or fill material' only. D issues a permit under section 404 either on a class-wide (general permit) or a case-by-case (individual permit) basis. D issues a general permit 'on a State, regional, or nationwide basis for any category of activities involving discharges of dredged or fill material.' Before issuing a general permit for a 'category of activities,' the Corps must 'determine that the activities in such category are similar in nature, will cause only minimal adverse environmental effects when performed separately, and will have only minimal cumulative adverse effect on the environment.' A general permit is limited to five years--and may be revoked or modified if the authorized activities 'have an adverse impact on the environment or . . . are more appropriately authorized by individual permits.' D's individual permit process is a longer, more comprehensive procedure. D makes a formal decision on an individual application following site-specific documentation and analysis, public interest review, public notice and comment, and, if necessary, a public hearing. An applicant may challenge any determination through an administrative appeals process and must exhaust his administrative remedies before heading to federal court. Nationwide permits (NWPs) are general permits designed to minimize delays and paperwork for projects with minimal environmental impact. There are currently 43 NWPs in force--covering activities ranging from 'Single-family Housing' (NWP 29) to 'Mining Activities' (NWP 44) to 'Cranberry Production Activities' (NWP 34)--that are subject to 27 General Conditions (GCs). In 1996, D proposed to reissue a number of existing NWPs, with modifications, that were otherwise set to expire on January 21, 1997. NWP 26 was on the list. D gave public notice of--and sought comment on--proposed changes to its 'pre-construction notification' timeline and acreage threshold limits. D decided to replace NWP 26 with 'activity-specific' general permits. It reissued NWP 26 for a two-year period but with more stringent conditions. In July 1998, D published a proposed suite of activity-specific general permits to replace NWP 26. In March 2000, following another round of public comment, D promulgated activity-specific permits consisting of five new NWPs and six modified NWPs, all intended to replace NWP 26. Ps sued D alleging (1) D exceeded its statutory authority under the CWA by imposing certain permit conditions; (2) D acted arbitrarily and capriciously, in violation of the APA, 5 U.S.C. § 706(2)(A), by failing to provide a rational basis for its permit acreage thresholds; (3) D violated the Regulatory Flexibility Act (RFA), 5 U.S.C. §§ 601 et seq., by failing to evaluate the potential impact of the permits on small businesses and other small entities as well as alternatives to the permits; and (4) D violated the National Environmental Policy Act (NEPA), 42 U.S.C. §§ 4321 et seq., by failing to prepare a Programmatic Environmental Impact Statement (PEIS) for the permits. The National Resources Defense Council and the Sierra Club (the intervenors) intervened in the district court proceedings in support of D. Everyone moved for summary judgment on February 15, 2001. The district court granted summary judgment to D because its acts did not constitute a 'final' agency action because no legally binding action has taken place as to any given project until either an individual permit application is denied or an enforcement action is instituted. Ps appealed.