San Luis Reservoir State Recreation Area © 2015, California State Parks. Photo by Brian Baer

The Department of the Interior and San Luis & Delta-Mendota Water Authority approved plans Friday to raise the dam at the San Luis Reservoir and expand its capacity.

The joint project will create an additional 130,000 acre-feet of storage space in San Luis Reservoir, the nation’s largest offstream reservoir, producing additional water supply for two million people, over one million acres of farmland and 135,000 acres of Pacific Flyway wetlands and critical wildlife habitat, according to a news release from the Delta-Mendota Water Authority.

The signing of the Record of Decision and Notice of Determination is the first approval of a major water storage project in California since 2011, according to the release.

A $25 million investment to the project under the federal Bipartisan Infrastructure Law was announced in October 2022 and an additional $10 million this past July. An additional $60 million was authorized for project construction from the Water Infrastructure Improvements for the Nation Act, for a total of $95 million in federal contributions to date in construction costs.

Previously, the Bipartisan Infrastructure Law provided more than $100 million to the reservoir’s B.F. Sisk Dam for a project currently under construction that will increase the dam crest by 10 feet to improve seismic safety. Leveraging this existing project, the Bureau of Reclamation and the Delta-Mendota Water Authority are partnering to add an additional 10 feet to the dam through Friday’s announcement to allow for expansion of the reservoir’s storage capacity.

The expanded space will store water that can be delivered to south-of-Delta water contractors and wildlife refuges.

“As California and the West deal with historic drought conditions, the Biden-Harris administration is working in close coordination with local communities, states and Tribes to build climate resilience and long-term water supply reliability for future generations,” said Principal Deputy Assistant Secretary for Water and Science Michael Brain.      

B.F. Sisk Dam is a 382-foot high earthfill embankment located on the west side of the Central Valley, about 12 miles west of Los Banos. The dam is over three miles long and impounds San Luis Reservoir, which has a current total capacity of around 2 million acre-feet of water.

After the previous wet winter, its current storage is 74% of capacity — 168% of its historic average.

“San Luis Reservoir has served as the hub of California’s water system south of the Sacramento San Joaquin Bay-Delta since its completion in 1967,” said San Luis & Delta-Mendota Water Authority Board Chair Cannon Michael. “The ability to capture more water in the years it is available, particularly given California’s changing climate, is a critical component of a more secure future for the communities, farms and wildlife dependent on the Central Valley Project for their water supply. We value our partnership with the Bureau of Reclamation and look forward to completion of this vital water storage project.”