The Wilkins Project (Project), a private marina, was proposed for a location near the Back Bay National Wildlife Refuge (Refuge). The United States Army Corps of Engineers (Corps) (defendant) prepared an environmental assessment for the Project, as required by the National Environmental Policy Act (NEPA). The United States Fish and Wildlife Service (FWS) suggested that the Corps prepare an environmental impact statement (EIS) under NEPA to address the Project’s adverse effects on wildlife and vegetation, including habitat loss associated with boating. Instead of preparing an EIS, the Corps established a restricted area called a no-wake zone (NWZ), and authorized the NWZ’s enforcement by federal, state, and local authorities. However, enforcement was problematic due to local staffing constraints. In September 2008, the Corps expressed the hope that compliance would result from education, signage, and public pressure. On October 3, 2008, the FWS conditioned its acquiescence to the Project on the NWZ’s adequate funding and enforcement. The Corps issued a permit for the Project on October 10, 2008, and issued a final environmental assessment (EA) along with the permit. Although the final EA stated that the NWZ would limit and reduce the Project’s adverse impacts, the permit did not mandate the NWZ’s enforcement or guarantee its funding. The EA resulted in a Finding of No Significant Impact (FONSI), which stated that no EIS would be prepared. The NWZ remained unmarked with signage, as well as unenforced. Friends of Back Bay and others (plaintiffs) brought a complaint against the Corps and various federal officials (defendants) in district court, claiming that the Corps should have prepared an EIS. Both parties filed cross-motions for summary judgment. The district court granted the defendants’ motion, and the plaintiffs appealed.