Folsom Lake is a reservoir in Northern California about 25 mi northeast of Sacramento in Placer, El Dorado, and Sacramento Counties. The lake is formed by Folsom Dam, constructed in 1955 to control the American River. The dam and lake are part of the Folsom Project, which also includes the Nimbus afterbay reservoir and dam facilities. The Folsom Project, operated by the United States Bureau of Reclamation, is part of the Central Valley Project, a multipurpose project that provides flood control, hydroelectricity, drinking water and water for irrigation. The Folsom Lake State Recreation Area is managed by the California Department of Parks and Recreation. When the dam was built it was designed to hold 1,010,000 acre feet with a surface area of 11,450 acres.
During the drought of late 2013, the town known as "Mormon Island" reappeared 58 years after being submerged under Folsom Lake, with stone walls from some of the outlying areas being revealed by the shrinking lake.