The State Water Project is the largest state-built water project in the United States. Its assets include the tallest dam in the United States, the largest off-stream reservoir in the United States, and the tallest water lift station in the world.

The project stretches nearly 600 miles from Northern California to Southern California and delivers an average of 2.4 million acre-feet of water through an interconnected system of 34 storage facilities, 20 pumping stations, four pumping and generating stations, five hydroelectric plants and approximately 700 miles of canals, tunnels and pipelines.

Operated by the California Department of Water Resources, water from the project serves urban customers in the Bay Area and Southern California and agricultural customers in the San Joaquin Valley. State Water Project water provides drinking water for 23 million people and irrigates 750,000 acres of farmland. About 70% of State Water Project water is for urban use and the remaining 30% is for agriculture.

The Path of the State Water Project

The State Water Project essentially begins at Lake Oroville, 70 miles north of Sacramento, where the 770-foot-high Oroville Dam, the tallest in the world, impounds the Feather River to form the 3.5 million acre-foot Lake Oroville. The dam is used for water storage, flood control, and recreational facilities. The stored water released by the dam flows down the Feather River and joins the Sacramento River, which flows into the Delta.

The Delta is the hub of California’s water infrastructure, a 700-mile-long labyrinth of marshes and waterways that encircles more than 60 levee trails and islands. The Delta is where the Sacramento River and the San Joaquin River meet and flow toward San Francisco Bay. Along the way, the freshwater rivers mix with the incoming tide to form the largest estuary on the West Coast. The Delta is home to over 750 species of animals and plants, many of which are threatened and endangered, as well as about 500,000 residents. At 738,000 acres, the Sacramento-San Joaquin Delta occupies only a fraction of the state’s land mass, but it plays a central role in the state’s ongoing water conflicts. You can learn more about this complicated place by clicking here.

The North Bay Aqueduct branches off from Barker Slough in the northern Delta to supply water to Napa and Solano counties; the remaining water flows south through the Delta to the Harvey O. Banks Pumping Station, where 11 pumps lift the water 244 feet and discharge it into the California Aqueduct.

As it travels south, part of the California Aqueduct is diverted into the South Bay Aqueduct to supply water to Silicon Valley and other Bay Area communities. The water continues south to the San Luis Reservoir, supplying irrigation water to the San Joaquin Valley and drinking water to communities in the Central Valley. South of Kettleman City, the Coastal Aqueduct branches off to supply San Luis Obispo and Santa Barbara.

The aqueduct continues to the foot of the Tehachapi Mountains, where fourteen pumps at the Edmonston Pumping Plant raise the water over the mountains. At the top, the aqueduct splits into the East and West Branch aqueducts, with the West Branch continuing to Pyramid and Castaic Lakes and the East Branch continuing south through the Antelope Valley to Silverwood Lake and Lake Perris. Depending on how many pumps are in operation, it takes 14 to 75 days for the water to travel the entire length of the California Aqueduct.

Construction of the project

After the end of World War II, a second “gold rush” occurred as new residents flooded into the state, attracted by the favorable climate and lured by the prospect of jobs. The growing population put pressure on the state to develop more water resources to stimulate economic growth.

In May 1951, State Engineer AD Edmonston proposed a dam on the Feather River at Oroville, a cross-delta canal, and aqueducts to supply water to southern Bay Area communities, the San Joaquin Valley, and Southern California. Additional plants were built in 1955 and 1957.

In 1959, the legislature passed the Burns-Porter Act, which authorized the issuance of $1.75 billion in bonds to finance the construction of the project. The vote on the issue in November 1960 was close, and the bill passed with only 173,944 votes out of 5.8 million.

After the measure passed, construction began in earnest and the Oroville Dam was completed in 1967. The South Bay Aqueduct was the first State Water Project delivery system to be completed. Water was delivered to Alameda County in 1962; water was to follow in Santa Clara County in 1965. The Delta plants were completed in 1968, but it wasn’t until the Edmonston Pumping Plant was completed in 1971 that water finally reached Southern California. By 1973, the first plants were completed. The Coastal Branch was completed in 1997.

Although the State Water Project uses falling water to generate hydroelectric power wherever possible, it produces only about two-thirds of the energy needed to operate its facilities, making it one of the state’s largest consumers of electricity.

State water supply companies

Twenty-nine water utilities have signed contracts for the long-term delivery of 4.2 million acre-feet of water. The Metropolitan Water District of Southern California is the largest contractor, entitled to just over 2 million acre-feet, or about 47% of the water delivered; Kern County is the second largest contractor, with 1.1 million acre-feet, or about 27% of the project’s total. The remaining 26% will be divided among the remaining 27 water utilities.

Although contractors are entitled to 4.2 million acre-feet of water, the State Water Project can only deliver between 2.5 and 3.5 million acre-feet on average. The lowest amount delivered was 0.55 acre-feet during the 1991 drought.

Benefits and impacts as well as future expansion

The State Water Project boosted California’s economic growth, enabled the rise of Silicon Valley and the growth of Southern California, and brought more farmland into production. But the project remains controversial. Critics say the water projects penalize those who live closest to rain and reward those who live farthest away. The export of large amounts of water from the Delta by the State Water Project and the Central Valley Project has impacted the Delta and put native species at risk, many of which are considered threatened and endangered.

The State Water Project was actually much larger, but so far only the first phase has been completed and it is unlikely that the other facilities will ever be built to the original specifications. There are several reasons for this: many of the Northern California rivers that were to be included in the system have since been protected as Wild & Scenic, any future expansion would be subject to extensive public review, and there are laws and regulations that reflect the changing societal values ​​that have come into effect since the project was first planned.

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This page was updated on August 14, 2024.