Eight California water agencies and the federal government agreed on Nov. 13 to share the costs of raising the B.F. Sisk Dam, which impounds the nation’s largest off-stream reservoir in the San Joaquin Valley.

The agreement dedicates nearly $1 billion to expanding the San Luis Reservoir, adding 130,000 acre-feet of storage. This will provide water for about two million people, over one million acres of farmland, and 135,000 acres of Pacific Flyway wetlands and wildlife habitat.

“The ability to capture more water in the years it is available, particularly given California’s dynamic hydrology, is a critical component of a more secure future for the communities, farms, and wildlife,” said San Luis & Delta-Mendota Water Authority Board Chair Cannon Michael in a statement.

The reservoir has reached full or near-full capacity during several recent wet years and is currently at 51 percent of its capacity as of Nov. 17, according to the California Department of Water Resources.

Completed in 1967, the B.F. Sisk Dam is currently undergoing construction to raise its more than 3.5-mile-long crest by 10 feet for improved seismic safety, funded in part by $100 million from the federal Bipartisan Infrastructure Law.

Construction is underway to improve the seismic reliability of B.F. Sisk Dam. (U.S. Department of the Interior Bureau of Reclamation)

Under the new agreement, an additional 10 feet will be added to further increase the reservoir’s capacity to store water during wet years, benefiting farmers in the San Joaquin Valley and Kern County. The dam’s existing 2 million acre-feet of storage also serves as a vital water source for the Metropolitan Water District of Southern California, supplying the Greater Los Angeles area.

The dam, jointly owned by the U.S. Bureau of Reclamation and the state Department of Water Resources, currently allocates 55 percent of its water to the state and 45 percent of its water to the federal government.

For the additional water the project brings, the federal government will cover 30 percent of the cost and receive 39,000 acre-feet, or 30 percent of the new storage capacity. The eight water agencies will provide 70 percent of the funding in exchange for 91,000 acre-feet.

As part of the agreement, the Santa Clara Valley Water District, serving 2 million residents in Santa Clara County, will provide $435 million toward the $942 million project. In exchange, the agency will secure 60,000 acre-feet of water, the largest portion of the expanded storage.

Other recipients of the water include the Westlands Water District in Fresno, the Byron Bethany Water District in Contra Costa County, the City of Tracy, the San Benito County Water District, and the Del Puerto, San Luis, and Pacheco water districts.

The project also involves rerouting more than one mile of Highway 152 away from the reservoir’s high-water shoreline to enhance safety, with an estimated cost exceeding $430 million.

Construction to raise the dam is set to begin in September 2025, during the final stages of seismic improvements, and is expected to be completed within eight years, according to the San Luis & Delta-Mendota Water Authority.

Gov. Gavin Newsom and state leaders joined water managers and federal officials in Washington on Nov. 13 as the federal Bureau of Reclamation announced the agreement.

The agreement marks the Reclamation’s first approval of a major water storage project in California since 2011, the agency said.

People fish below the high water marks (background) of the San Luis reservoir which is at only 21 percent capacity as a severe drought continues to affect California on Sept. 23, 2014. (Mark Ralston/AFP via Getty Images)

California has endured several severe droughts in recent years, including from 2007 to 2009, which prompted the state’s first-ever statewide emergency proclamation; 2011 to 2017, one of its longest drought periods; and 2020 to 2022.

In response, the Biden administration and Newsom have advocated building more reservoirs to capture water during wet years, aiming to mitigate the effects on urban areas, agriculture, and wildlife during dry periods.

Rick Callender, CEO of Valley Water, echoed the idea in the statement that “investing in water infrastructure, including surface storage, is needed now more than ever to become more drought resilient.”

Water infrastructure projects in California have consistently faced challenges, whether due to financial constraints or opposition from environmental groups.