O'Neill Forebay is a man-made reservoir located in California's Central Valley. Its construction was completed in 1967 and it serves as a part of the State Water Project, which supplies water to various regions of California. The reservoir's primary source of water is the San Luis Reservoir, which is fed by surface water flows from the Sacramento-San Joaquin Delta and snowmelt from the Sierra Nevada Mountains. The reservoir also receives additional water from the California Aqueduct. O'Neill Forebay is used for agricultural irrigation and provides water to nearby farms. It is also a popular destination for recreational activities such as boating, fishing, and camping. The reservoir holds a capacity of 93,000 acre-feet of water and is operated by the California Department of Water Resources.