Methow Recreation, Inc. (MRI) applied to the Forest Service (defendant) for a special-use permit to develop and run a ski resort on a mountain located in a national forest in Washington. Pursuant to the National Environmental Policy Act of 1969 (NEPA), the Forest Service commissioned an environmental impact statement (EIS) to consider the effects of the resort on wildlife and outline possible mitigation measures. The EIS ultimately recommended a permit be issued for a 16-lift ski area with capacity for 8,200 skiers. The Forest Service's Regional Forester issued the permit as recommended by the EIS. Methow Valley Citizens Council and other organizations (plaintiffs) appealed the Regional Forester's decision to the Chief of the Forest Service (Robertson), who affirmed the decision. Plaintiffs brought an action under the Administrative Procedure Act (APA) for judicial review of Robertson's decision, claiming that the EIS did not satisfy NEPA's requirements. After a trial, a United States Magistrate Judge found that the EIS was adequate. The judge concluded that the EIS had sufficiently assessed the project's adverse impacts on the mule-deer population and air quality, and that the EIS contained a sufficient discussion of mitigation measures. The appellate court reversed and found the EIS inadequate. Specifically, the appellate court held that the Forest Service could not conclude that the impact on the mule-deer population would be minor as a result of the Forest Service's mitigation efforts, as the mitigation efforts had not yet been implemented or even developed. The court held that if the Forest Service could not adequately determine the impact on a population, it had a duty to make an analysis based on the worst-case scenario. Further, the court concluded that the Forest Service was required to fully develop mitigation measures before granting a permit and that the EIS must include a thorough discussion of mitigation measures.