Section 10(j)(1) of the Federal Power Act (FPA), 16 U.S.C. § 803(j)(1), required hydropower licenses issued by the Federal Energy Regulatory Commission (FERC) (defendant) to include conditions to protect fish and wildlife. These conditions were to be based on recommendations from the National Marine Fisheries Service, the United States Fish and Wildlife Service, and state fish and wildlife agencies. Section 10(j)(2) of the FPA contained a qualifying clause that allowed FERC to publish findings that any submitted conditions were inconsistent with the FPA. Section 18 of the FPA, 16 U.S.C. § 811, directed FERC to require licensees to create fishway mechanisms to protect migrating fish, upon the request of the secretaries of the interior or commerce (secretaries). Section 18 did not contain a qualifying clause. FERC issued a hydropower license to the Eugene Water and Electric Board without including conditions submitted by state and federal fish and wildlife agencies under §§ 10(j)(1) and 18 of the FPA. American Rivers and a coalition of environmental organizations (plaintiffs) sought a rehearing before FERC, which denied their request. The plaintiffs petitioned the United States Court of Appeals for the Ninth Circuit for review, claiming that FERC’s failure to include the submitted conditions violated §§ 10(j)(1) and 18 of the FPA. Specifically, the plaintiffs argued that (1) the FPA did not allow FERC to reject fish and wildlife agency recommendations submitted under §§ 10(j)(1), and (2) the FPA did not allow FERC to reject fishway prescriptions proposed under § 18. FERC claimed that its inability to reject the conditions would compromise its statutory mission, and that the fishway regulations did not specify which agency was responsible for determining if a given prescription constituted a fishway.