Oroville Dam is the centerpiece of the State Water Project (SWP) and its largest water storage facility.

Located about 70 miles north of Sacramento at the confluence of the three forks of the Feather River, Oroville Dam is an earthfill dam (consisting of an impervious core surrounded by sands, gravels and rockfill materials) that creates a reservoir that can hold 3.5 million acre-feet of water.

Features such as a fish barrier dam and pool at Oroville Dam made the State Water Project one of the first major water projects built with environmental protections as a significant consideration. The reservoir created by the dam provides major water recreation facilities for boating, fishing and camping.

Besides storing water, the dam also protects downstream residents from the flood-prone Feather River – the main feeder of the State Water Project, which sends water all the way to Southern California and serves 27 million people and 4 million to 5 million acres of farmland along the way. 

Water stored behind Oroville Dam helps California withstand periodic droughts that grip the state. But a severe two-year drought by early October 2021 had cut water storage behind Oroville Dam to just 22 percent of capacity.

Oroville Dam Background

Oroville Dam’s Edward Hyatt Powerplant is also the largest SWP hydroelectric facility, and has the capacity to generate 819 megawatts of electricity. A megawatt produces electricity roughly equal to the same amount of electricity consumed by 400 to 900 homes in a year.

Construction began on facilities related to Oroville Dam in 1957 and on the dam site itself in 1961. Within a few years, the partially completed dam checked flooding on the Feather River in December 1964, saving the Sacramento Valley. 

Oroville Dam is the tallest dam in the U.S. at 770 feet (slightly shorter than the Transamerica Pyramid in San Francisco, which is 853 feet tall).

Oroville Dam Operations

Stored water released from Oroville Dam flows down the Feather River and enters the Sacramento River system near Verona.

About one-third of the water released from the reservoir goes to uses between Oroville and the Sacramento-San Joaquin Delta. When it reaches the Delta, Feather River water blends with snowmelt and runoff from other watersheds of the Sacramento and San Joaquin valleys. At Barker Slough, in the North Delta, up to 76,781 acre-feet of water can be diverted into the North Bay Aqueduct, a 27.6-mile underground pipeline that provides water to augment local supplies in Napa and Solano counties.

More problematic, Oroville Dam blocked salmon and steelhead trout access to upstream spawning areas, though many of the fish have adapted to spawning in gravel beds below the dam. To further mitigate fisheries impacts, a barrier and ladder system was built that allows adult salmon and steelhead to be captured at the Feather River Fish Hatchery, then artificially spawned and later released in the Delta or Sacramento River.

When high inflows occur between October and May, water is held in Lake Oroville temporarily until downstream channels are capable of handling them without flooding. Oroville Dam alone provides 750,000 acre-feet of flood control storage. The dam has been credited with minimizing damage during floods that have hit the Feather River watershed in virtually every decade since the dam’s construction in the 1960s.

In early 2017, substantial runoff from the Sierra Nevada filled up Lake Oroville, forcing the release of a large volume of water down the dam’s concrete spillway. The force of the release gouged a large crater in the concrete spillway and required the California Department of Water Resources (DWR) to halt water releases via that conduit.

The high lake level strained the earthen emergency spillway and eventually there was fear that erosion would compromise the integrity of the auxiliary spillway and flood the city of Oroville and surrounding communities. An evacuation order forced thousands of people to seek higher ground.

Ultimately, an independent analysis concluded that poor design and construction and inadequate state oversight contributed to the collapse of the concrete spillway. After an accelerated repair, the 3,000-foot main spillway was completed in time for the winter 2017 runoff, with additional phases of work focused on concrete seams, drainpipes, drain seams, cleanup and the emergency spillway and cutoff wall below. On April 2, 2019, water flowed for the first time down the rebuilt spillway. Reconstruction of the main and emergency spillways cost $1.1 billion.

In 2020, an independent review board convened by DWR determined that the dam and its associated facilities are safe to operate and that no urgent repairs are needed. The assessment, initiated in 2018 to identify dam safety and operational needs, identified several risk-reduction projects that DWR is working on, including installation of new water pressure measurement devices to improve seepage monitoring and completion of a state-of-the-art seismic stability analysis.

Feather River Fish Hatchery

The hatchery was built by DWR and paid for by the agencies that buy water from the SWP to mitigate for upper Feather River spawning areas lost to the creation of Lake Oroville. Fish raised at the hatchery or spawned in the Feather River account for an estimated 20 percent of the ocean sport and commercial catch of salmon and steelhead in the Pacific Ocean. The hatchery is run by the state’s Department of Fish and Wildlife.

FERC Relicensing

The Federal Energy Regulatory Commission, commonly known as FERC, licenses hydroelectric facilities such as the Edward Hyatt Power Plant at Oroville Dam.

DWR and stakeholders participated in a six-year renewal process for a 50-year hydroelectric license for the Oroville facilities. If adopted by FERC, the resulting agreement commits the state to:

• Restored salmon and steelhead habitat
• Improved river recreation and community benefits
• A fish passage study to determine and launch a project to enhance fish passage in the Feather and surrounding river basins