Lake Oroville and Oroville Dam are part of a complex which includes Hyatt Powerplant, Thermalito Diversion Dam and Powerplant, the Feather River Fish Hatchery, Thermalito Power Canal, Thermalito Forebay, Thermalito Pumping- Generating Plant, Thermalito Afterbay, and the Lake Oroville Visitors Center.

The Oroville-Thermalito Complex was designed as a water and power system. It stores about 3.5 million acre-feet and generates power from releases made through Hyatt Powerplant and two other Thermalito generating plants. A special fish barrier dam was built to lead salmon and steelhead, returning to spawn, into the Feather River Fish Hatchery.

Water released from Lake Oroville is used to produce electricity by Hyatt Powerplant, located in the bedrock beneath Oroville Dam. Water can either enter the Feather River or be diverted by the Thermalito Diversion Dam.

Water diverted is used to generate power by the one-unit Thermalito Diversion Dam Powerplant. From there the water enters the Thermalito Power Canal and flows into Thermalito Forebay. At the end of the forebay, water enters the Thermalito Afterbay and is used by the Thermalito Pumping-Generating Plant to produce electricity.

The plant can also pump water back to the lake to be reused for power generation at Hyatt Powerplant.

The Feather River Fish Hatchery and the Fish Barrier Pool are located along the Feather River below the lake and the visitors center is located near Lake Oroville.

Lake Oroville

Oroville Dam and Lake Oroville lie in the foothills on the western slope of the Sierra Nevada, one mile downstream of the junction of the Feather River’s major tributaries.

The lake stores winter and spring runoff which is released into the Feather River to meet the Project’s needs. The reservoir has a Maximum Operating Storage (mos) of 3,537,580 acre-feet. It also provides pumped-storage capacity, 750,000 acre-feet of flood control storage, recreation, and freshwater releases to control salinity intrusion in the Sacramento-San Joaquin Delta and for fish and wildlife protection.

Construction first began in 1957 to relocate what is now Highway 70 and the Union Pacific Railroad. Work on the dam site began in 1961. The embankment was topped out in 1967, and the official dedication ceremony was held the next year.

Hyatt Power Plant

Located in rock in the left abutment near the axis of Oroville Dam, Edward Hyatt Powerplant is an underground, hydroelectric, pumping-generating facility. Construction of the plant began in 1964 and was completed in 1967.

Hyatt Powerplant maximizes power production through a pumped-storage operation where water, released for power in excess of local and downstream requirements, is returned to storage in Lake Oroville during off-peak periods and is used for generation during peak power demands.

Water from the lake is conveyed to the units through penstocks and branch lines. After passing through the units, water is discharged through the draft tubes to one free surface and one full-flow tailrace tunnel.

The facility was named for Edward Hyatt, who was State Engineer (1927-1950) of the Division of Water Resources under the Department of Public Works. The Division was the predecessor to the Department of Water Resources

The power plant has a generation capacity of 645 megawatts.

Thermalito Facilities

Thermalito Diversion Dam and Pool

Constructed between 1963 and 1968, the Thermalito Diversion Dam and Pool are located on the Feather River, about 4.5 miles downstream from Oroville Dam.

The dam diverts water in Thermalito Power Canal for power generation at Thermalito Pumping Generating Plant and creates a tailwater pool for Hyatt Powerplant.

The reservoir also acts as a forebay when Hyatt Powerplant is pumping water back into Lake Oroville. It also provides recreation opportunities.

The diversion dam has a maximum operating storage (mos) of 13,350 acre-feet.

Thermalito Diversion Dam Powerplant

Thermalito Diversion Dam Powerplant is located at Thermalito Diversion Dam below the left abutment of the dam.

The powerplant generates electricity from water released to the Feather River to maintain fish habitat between the diversion dam and Thermalito Afterbay river outlet. It was constructed between 1985 and 1987.

The powerplant has a generating capacity of 3.4 megawatts.

Thermalito Forebay

Constructed between 1965 and 1968, Thermalito Forebay is an offstream reservoir contained by Thermalito Forebay Dam on the south and east and by Campbell Hills on the north and west. It is located about four miles west of the city of Oroville.

The forebay conveys generating and pumping flows between Thermalito Power Canal and Thermalito Powerplant, provides regulatory storage and surge damping for the Hyatt-Thermalito power complex, and serves as a recreational site.

The forebay has a maximum operating storage of 11,770 acre-feet.

Thermalito Pumping-Generating Plant

Located about four miles west of the city of Oroville in Butte County, Thermalito Pumping-Generating Plant is a principal feature of the Oroville-Thermalito pumped storage power complex. A pumping-generating plant, the facility is operated in tandem with Hyatt Powerplant and Thermalito Diversion Dam Powerplant to produce power.

Water released for power in excess of local and downstream requirements is conserved by pumpback operation during off-peak hours through both power plants into Lake Oroville to be subsequently released for power generation during periods of peak power demand. Construction on the plant began in 1964 and was completed in 1969, with operations starting in 1968.

The pumping-generating plant has a generating capacity of 114 megawatts.

Thermalito Afterbay

Located about six miles southwest of the city of Oroville, Thermalito Afterbay is an offstream reservoir.

The afterbay provides storage for the water required by the pumpback operation to Lake Oroville, helps regulate the power system, produces controlled flow in the Feather River downstream from the Oroville-Thermalito facilities, and provides recreation. It also serves as a warming basin for agricultural water delivered to farms east of the afterbay.

Thermalito Afterbay Dam has the longest crest in the SWP system. The facility was constructed from 1965 to 1968.

The afterbay has a maximum operating storage of 57,040 acre-feet.