The San Luis Reservoir is an artificial lake on San Luis Creek in the eastern slopes of the Diablo Range of Merced County, California, approximately 12 mi (19 km) west of Los Banos on State Route 152, which crosses Pacheco Pass and runs along its north shore.

Completed in 1967 on land formerly part of Rancho San Luis Gonzaga, the 12,700 acres (5,100 ha) reservoir is a joint use facility, being a part of both the California State Water Project and federal Central Valley Project, which together form a network of reservoirs, dams, pumping stations, and 550 miles (885 km) of canals and major conduits to move water across California.

Those 500 kV wires, carrying both the power generated here and elsewhere, leave the area and cross the O'Neill Forebay on several man-made islands.

San Luis Reservoir also supplies water to 63,500 acres (25,700 ha) of land in the Santa Clara Valley west of the Coast Ranges.

Improved boat launch ramps are offered at Dinosaur Point and the Basalt area.

Due to the reservoir's water being imported from the Sacramento River Delta, San Luis shares many of its fish species with that area, including largemouth bass, striped bass, crappie, bluegill, shad, yellow perch, and occasional sturgeon and salmon.

The California Office of Environmental Health Hazard Assessment (OEHHA) has developed a safe eating advisory for fish caught in the San Luis Reservoir based on levels of mercury or PCBs found in local species.