Background
The Nimbus Fish Hatchery (NIM) is operated by the California Department of Fish and Wildlife under contract with the United States Bureau of Reclamation (Reclamation). The purpose of the hatchery programs is to mitigate for salmon and steelhead spawning and rearing habitat eliminated due to construction of Nimbus Dam in 1955, and to support river and ocean fisheries.
The NIM conducts an artificial propagation program for fall-run Central Valley (CV) Chinook salmon and steelhead trout on the lower American River. The California Department of Fish and Wildlife lists the CV fall-run Chinook salmon as a Species of Special Concern and the National Marine Fisheries Service (NOAA) lists the CV fall run Chinook as a Species of Concern. NOAA has listed natural origin CV steelhead as a threatened species. Hatchery origin steelhead at NIM are not considered to be part of the steelhead CV evolutionary significant unit (ESU) and for that reason are segregated from natural origin steelhead returning to the hatchery.