 As part of the Central Valley Project (CVP), a federal water project that provides irrigation and municipal water to much of California's Central Valley, it was authorized in 1949 as a regulating reservoir for Folsom Dam, and a diversion pool for the Folsom South Canal.Construction began in 1952, and it opened in 1955.The Nimbus Powerplant is located on the north side of the American River and on the left side of Nimbus Dam via looking east.