The Schellingers (defendants) owned land in California that they sought to develop. A portion of the land was designated as “adjacent wetlands” under the Clean Water Act (CWA), 33 U.S.C. §§ 1251-1387. The Schellingers applied for a CWA permit to discharge pollutants into the wetlands. Around this time, an amateur naturalist discovered Sebastopol meadowfoam in the wetlands. The meadowfoam was listed as an endangered plant under the Endangered Species Act (ESA), 16 U.S.C. §§ 1531 et seq. The California Department of Fish and Game (CDFG) (defendants) removed meadowfoam from the land as part of an investigation. Northern California River Watch (River Watch) (plaintiff) filed a complaint against the Schellingers and various CDFG employees (defendants) for taking the meadowfoam in violation of § 9 of the ESA, which prohibited the removal of endangered plant species in areas of federal jurisdiction. River Watch claimed that the wetlands were areas of federal jurisdiction because they were under the CWA’s jurisdiction. The defendants filed a motion for summary judgment, arguing that areas of federal jurisdiction encompassed only federally owned land. The district court granted the defendants’ motion, and River Watch appealed. The United States, participating as amicus curiae, argued that the rules and a manual of the U.S. Fish and Wildlife Service (FWS) clarified the ambiguity and should receive deference under Chevron, U.S.A., Inc. v. Natural Resources Defense Council, Inc., 467 U.S. 837 (1984).