| O'Neill Forebay | |
|---|---|
 O’Neill Forebay and Dam as seen from left bank | |
  O'Neill Forebay | |
| Location | Merced County, California |
| Coordinates | 37°05′00″N 121°02′33″W / 37.0832°N 121.0426°W |
| Type | Reservoir |
| Primary inflows | California Aqueduct Delta–Mendota Canal San Luis Reservoir |
| Primary outflows | California Aqueduct |
| Catchment area | 18 acres (7.3 ha) |
| Basin countries | United States |
| Max. length | 3 km (1.9 mi) |
| Max. width | 3 km (1.9 mi) |
| Surface area | 2,250 acres (910 ha) |
| Max. depth | 17 m (56 ft) |
| Water volume | 56,400 acre-feet (69,600 dam3) |
| Shore length1 | 19 km (12 mi) |
| Surface elevation | 71 m (233 ft) |
| References | U.S. Geological Survey Geographic Names Information System: O'Neill Forebay |
| 1 Shore length is not a well-defined measure. | |
O'Neill Forebay is a forebay to the San Luis Reservoir created by the construction of O'Neill Dam across San Luis Creek approximately 12 miles (19 km) west of Los Banos, California, United States, on the eastern slopes of the Pacific Coast Ranges of Merced County.