Located in Merced, California, O'Neill Forebay is a federal-owned reservoir with a primary purpose of hydroelectric power generation. Constructed in 1967 by the Bureau of Reclamation, this earth dam stands at a height of 88 feet and has a storage capacity of 64,800 acre-feet. The reservoir covers a surface area of 2,250 acres and is fed by the San Luis Creek, with a maximum discharge capacity of 3,250 cubic feet per second.

With a hazard potential rated as high and a moderate risk assessment, O'Neill Forebay has undergone modifications in 1992 to strengthen its foundation, seismic resilience, and overall structural integrity. Despite its age, the dam's condition assessment is currently not available, and further risk management measures are yet to be specified. Managed by the Bureau of Reclamation, this reservoir plays a crucial role in water resource management and hydroelectric power generation in the region, showcasing the intersection of water infrastructure and climate resilience.