The California Department of Water Resources said Wednesday, Sept. 30, 2026, that it has completed a $235 million project to rehabilitate Oroville Dam’s river valve outlet system, which allows the department to release cold water from the deeper portions of Lake Oroville into the Feather River.

The system is located deep within one of the dam’s early diversion tunnels, DWR said; colder releases can help reduce downstream water temperatures and support fish populations during extreme heat and drought, including at the Feather River Fish Hatchery.

Construction started in October 2022, and commissioning of the valve system was completed in June, according to the department. Construction firms Syblon Reid of Folsom and The Dutra Group of San Rafael formed a joint venture to complete the work.

“Rehabilitating the RVOS was highly complex,” said Jason Brabec, DWR principal engineer and project manager. “It required immense coordination with contractors in a small space,” he said, adding that the work had to ensure Hyatt Powerplant met its green energy commitments and cold-water release requirements. He said the project required barges to transport valves, materials and equipment, and temporary bulkheads to permit work on valve infrastructure.

“This investment in Oroville Dam’s infrastructure ensures the reliable and safe operation of the State Water Project’s largest flood protection and water supply facility,” said John Yarbrough, deputy director of DWR’s State Water Project. “DWR will continue to prioritize modernization projects to improve aging infrastructure in an ever-changing climate.”

Oroville Dam, the tallest dam in the United States at 770 feet, was constructed between 1961 and 1967 and is a cornerstone of the State Water Project, according to DWR. The department said it operates the Oroville-Thermalito Complex to support Central Valley fish populations, including Chinook salmon and steelhead trout, which spawn each year in the Feather River below the dam.

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California Department of Water Resources

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