The proposed Sites Reservoir would be a 1.5 million-acre-foot off-river storage basin on the west side of the Sacramento Valley, about 78 miles northwest of Sacramento. It would capture stormwater flows from the Sacramento River for release in dry years for fish and wildlife, farms, communities and businesses.

The water would be held in a 14,000-acre basin of grasslands surrounded by the rolling eastern foothills of the Coast Range. Known as Antelope Valley, the sparsely populated area in Glenn and Colusa counties is used for livestock grazing.

The reservoir would be owned by the Sites Project Authority, a group of Sacramento Valley agricultural interests, cities and water districts, and operated in coordination with other Northern California reservoirs such as Shasta, Oroville and Folsom. Proponents hope the reservoir can begin operation by 2033. 

BACKGROUND

The reservoir takes its name from a small community in the basin that was home to John Sites, a pioneer rancher in the late 19th century. Though the reservoir would inundate the basin, many residents support the water storage proposal. The area where the 13-mile-long reservoir would be built also holds relics of Native American settlements, burial grounds and sacred sites, mainly those of the Patwin people

First conceived in the 1950s, Sites Reservoir emerged in the 1980s as part of a proposed second stage of the State Water Project, but the plan was abandoned.

Interest in the reservoir renewed in the 2000s as the frequency and severity of droughts grew under climate change and declines in native fish populations led to tighter restrictions on exporting water from the Sacramento-San Joaquin Delta.

The current proponent is the Sites Project Authority, whose board consists of representatives of Sacramento Valley water interests, including Colusa and Glenn counties, the Colusa County Water District, Glenn-Colusa Irrigation District, Tehama-Colusa Canal Authority, Westside Water District, Reclamation District 108, the cities of Roseville and Sacramento, Sacramento County Water Agency and Placer County Water Agency.

The project includes a reservoir committee of water agencies and irrigation districts across the state investing in a share of the water.

If the reservoir is built, the foothills would provide a natural barrier to the basin and facilitate the flooding of the long and narrow Antelope Valley. The reservoir would be fortified by several dams connecting the hills. The main dams, Sites and Golden Gate, would be built across Stone Corral and Funks creeks. Golden Gate Dam, the larger of the two, would stand about 287 feet high. Sites Dam would be about 20 feet lower at 267 feet. Six smaller saddle dikes would be built at the north end of the lake, according to the Bureau of Reclamation.

CHALLENGES AND CONTROVERSIES

Sites Reservoir is designed to achieve the following objectives when operated in coordination with existing Northern California reservoirs:

• Improve water supply reliability for agricultural, urban and environmental uses
• Increase anadromous and endemic fish populations
• Improve environmental and drinking water quality in the Delta

In dry years, the reservoir would help preserve the colder water in Lake Shasta to help critically endangered salmon and improve water quality in the Sacramento River, according to the Sites Project Authority.

Proponents say they favor the project because it would increase the flexibility and reliability of the State Water Project and federal Central Valley Project. Though Site Reservoir would not dam a river or block fish migration, critics say diversions for the reservoir could at times take more than 60 percent of the Sacramento River flows, potentially harming the river’s riparian and aquatic ecosystems and the many fish and wildlife species that depend on them. 

Two of the project’s challenges have been acquiring the money to build the project and securing a water rights permit from the State Water Resources Control Board.

In 2020, in part to make the project more affordable, the Sites Reservoir was reduced in size from 1.8 million acre-feet to 1.5 million acre-feet, dropping the reservoir’s average delivery capacity from 505,000 to 243,000 acre-feet a year. The modified plan also eliminated an 18-mile pipeline to the Sacramento River. Instead, the river would be diverted to the reservoir through the Tehama-Colusa and Glenn-Colusa canals and released back into the river to augment natural flows and releases from other reservoirs.

Those actions reduced the estimated costs at the time from $5.1 billion to $3 billion. Since then, costs have grown and the project is now projected to cost $6.4 billion to $6.8 billion.

The Sites project has gained critical financial support from state and federal agencies. The federal government through the Bureau of Reclamation has committed $798 million for Sites and the state has awarded nearly $1.1 billion for the project. Most of the state’s funding is from Prop. 1, a 2014 voter-approved water bond designed in part to support water storage projects. The project also has qualified for a $2.2 billion low-interest loan through the U.S. Environmental Protection Agency. Local agencies up and down the state are expected to fund the rest. Nearly 30 local water agencies have agreed to participate in the project.

Since 2017, Metropolitan Water District of Southern California has invested about $31 million into the planning, permitting and environmental review effort for Sites Reservoir. Metropolitan’s board will have to consider any future investment.

One hurdle to moving forward with the project may be getting a water right from the State Water Resources Control Board (State Water Board) to take the river water needed to fill the reservoir. The Sites Project Authority is seeking a permit to divert as much as 1.5 million acre-feet from the Sacramento River from September 1 through the following June 14 each year – a period when, depending on precipitation patterns, river flows are likely to be at their highest levels. The State Water Board held hearings in 2024 and 2025 on whether to grant the permit. A decision is pending.

LOOKING AHEAD

Sites Project Authority in January 2026 signed a construction contract with Barnard Construction Co. of Bozeman, Montana, to begin preliminary pre-construction work. If the Sites Project Authority is granted a water rights permit and the local agencies that have signed on to the project fulfill their funding commitments, construction could begin in 2027 and continue until 2033.

Updated February 2026