|Primary outflows||Stone Corral Creek, Funks Creek|
|Managing agency||California Department of Water Resources|
|Built||2023 start; 2030 completion (proposed)|
|Max. length||13 miles (21 km)|
|Surface area||14,000 acres (5,700 ha)|
|Max. depth||310 ft (94 m)|
|Water volume||1.8×106 acre feet (2.2 km3)|
(max. as proposed)
|Surface elevation||580 ft (180 m)|
Sites Reservoir is a proposed $5.2-billion offstream reservoir project west of Colusa in the Sacramento Valley of northern California, to be built by the California Department of Water Resources. The project would pump 470,000 to 640,000 acre feet (580,000,000 to 790,000,000 m3) per year of the winter flood flow from the Sacramento River upstream of the Sacramento–San Joaquin River Delta, through existing canals to an artificial lake 14 miles (23 km) away. Annual yield will depend on precipitation and environmental restrictions.
Preliminary studies were conducted at a cost of $50 million during 1996–2014. In 2018, the state awarded the reservoir project $820 million from a bond (Proposition 1), half the funding originally sought. Project backers were displeased with the funding shortfall. Additional funding was tentatively pledged from water agencies ("agricultural districts") in the Sacramento Valley, Fresno and urban agencies including Los Angeles. Each agency will be entitled to store water in the lake, in proportion to its share of the construction funding. In view of the shortfall, the pledges are being reassessed.
The reservoir would be reduced in size if funding were cut back, but backers believe the project would still be built. As of 2020[update], construction was to begin in 2023 and be completed in 2030.
The state will fund 16% or $820 million of the $5.2 billion project in exchange for rights to nine percent of the yield or 50,000 acre feet (62,000,000 m3) per year, to protect habitat for endangered Delta smelt and for wildlife refuges.
The Sites Reservoir was proposed in the 1980s. California had serious droughts in 2006–2010 and 2011–2017, raising concern about water insecurity. The project is intended to improve reliability of supply during drought conditions.
Cost and funding
The estimated cost of the reservoir is $5.2 billion. In 2018, the state awarded $820 million from a bond (Proposition 1) to the reservoir project. About 30 water agencies in California have tentatively committed funding.
The high cost of storage has led irrigation districts in the Sacramento Valley to reduce their funding and share of ownership. Water agencies in southern California and the San Joaquin Valley have increased their share. Crops grown in the San Joaquin Valley, such as pistachios and almonds, have a higher value than typical crops in the Sacramento Valley. The San Joaquin Valley and urban agencies can afford to acquire higher-cost water. However, by state law, agencies in the Sacramento Valley control the entire governing board for the project.
The federal Bureau of Reclamation could put $1 billion into the project.
The 14,000-acre (5,700 ha) reservoir would be formed by several dams located in the east foothills of the California Coast Ranges, flooding the long and narrow Antelope Valley. The main dams, Sites and Golden Gate, would be built across Stone Corral and Funks Creeks, respectively. Six smaller saddle dikes would hold in the north end of the lake. The total capacity would be between 1.3 to 1.8 million acre feet (1.6 to 2.2 km3).
Capacity could be expanded in the future, by raising the surrounding dikes.
The project is a pumped-storage hydroelectric plant, similar to San Luis Reservoir in the San Joaquin Valley, and would be a net power consumer; however, it would be able to generate peaking power. It will provide large-scale grid energy storage.
The proposed reservoir is not located on a major river but would affect salmon fisheries, because as part of California infrastructure to provide water to state agricultural interests it would impound water diverted from salmon-bearing watersheds, particularly the Trinity River via Lewiston Dam, with major negative impacts to imperiled salmon species already diminished by current and past water diversions to agriculture far from the sensitive watersheds of the north state. The state government's planning had not taken these impacts to threatened and endangered species into account as of early 2020.
Diversions could take 60 percent of the Sacramento River's flow at times, potentially harming salmon and other fish. (The Sacramento River's flows include water allocated from the Trinity and other northern tributaries, despite harm to salmon runs in source watersheds.) The reservoir itself would affect habitat for 23 sensitive, threatened or endangered wildlife species. Evaporation from the 14,000 acres (5,700 ha) reservoir would remove 30,000 acre feet (37,000,000 m3) per year.
According to "Final Feasibility Report" submitted by the Bureau of Reclamation in December 2020 : "A substantial portion of the project’s water would be specifically dedicated to environmental uses, helping to improve conditions for Delta smelt, preserving the cold-water pool in Lake Shasta to support salmon development, spawning and rearing, and providing a reliable water supply to improve the habitat for migratory birds and other native species." . 
To protect fisheries, the pumping stations along the Sacramento River will have fish screens. There are potential modifications upstream at Shasta Dam that could increase the supply of cold water. The intakes at the Tehama-Colusa and Glenn-Colusa Canals will be modified.
State regulators announced environmental restrictions in 2018 that would limit river withdrawals to protect fish, but environmental protections are under attack by the current federal administration and the state has not included strong protections in infrastructure plans. The water supply could fall short of projections.
- "Sites Reservoir: Frequently Asked Questions" (PDF). California Department of Water Resources. September 2007. Archived from the original (PDF) on April 1, 2014. Retrieved March 16, 2014. CS1 maint: discouraged parameter (link)
- "Water Storage Investment Program Project Review Portal". cwc.ca.gov. Retrieved 6 March 2018. CS1 maint: discouraged parameter (link)
- "Bureau of Reclamation releases progress report on Sites Reservoir". Maven's Notebook. December 31, 2013. Retrieved 2014-03-16. CS1 maint: discouraged parameter (link)
- "Our View: Sites Reservoir would sure come in handy this year". Appeal-Democrat. January 12, 2014. Retrieved 2014-03-16. CS1 maint: discouraged parameter (link)
- Hacking, Heather (March 27, 2014). "Sites Reservoir: A long time in coming, a long way to go". Chico Enterprise-Record. Retrieved April 24, 2014. CS1 maint: discouraged parameter (link)
- Dale Kasler and Ryan Sabalow (July 24, 2018). "California's largest reservoir project in decades gets an $800 million boost. But is it feasible?". Retrieved September 4, 2018. CS1 maint: discouraged parameter (link)
- Mike Luery (January 12, 2017). "5 things to know about the proposed Sites Reservoir". Retrieved January 4, 2020.
- Rogers, Paul (2020-05-11). "Massive Northern California reservoir project scaled back to reduce costs". The Mercury News. Retrieved 2020-05-11.
- Adam Kotin and Dru Marion (February 5, 2014). "A History of Drought in California: Learning From the Past, Looking to the Future". Retrieved January 7, 2020. CS1 maint: discouraged parameter (link)
- Dale Kasler and Ryan Sabalow (February 15, 2019). "Sites Reservoir is Sacramento Valley's water project. But L.A. is taking a huge role". Retrieved January 4, 2020.
'The reality is, the cost of water is going to be terrifically expensive,' said Durst, the board chairman. Durst’s own water agency, Reclamation District 108, has reduced its contribution to the project by 80 percent. The expense is less of a problem for San Joaquin Valley farmers, who generally grow higher-value crops such as almonds and pistachios and can afford costly water. It’s also less of a problem for Metropolitan, which can spread the cost among its 19 million urban customers.CS1 maint: discouraged parameter (link)
- "North-of-the-Delta Offstream Storage Feasibility Investigation: Fact Sheet" (PDF). U.S. Bureau of Reclamation and California Department of Water Resources. Northern California Water Association. June 2011. Retrieved March 16, 2014. CS1 maint: discouraged parameter (link)
- "Surface Storage". Northern California Water Association. Retrieved 2014-03-17. CS1 maint: discouraged parameter (link)
- Evans, Steven L. (August 2013). "Sites Offstream Storage Reservoir Fact Sheet" (PDF). Friends of the River. Retrieved March 17, 2014. CS1 maint: discouraged parameter (link)
- Zito, Kelly (September 29, 2009). "Water interests argue new state dam proposals". SFGate. Retrieved March 17, 2014. CS1 maint: discouraged parameter (link)
- "Sites Reservoir reaches milestone". Daily Democrat. 2020-12-25. Retrieved 2020-12-25.
- Dale Kasler and Ryan Sabalow (February 15, 2019). "Sites Reservoir is Sacramento Valley's water project. But L.A. is taking a huge role". Retrieved January 8, 2020. CS1 maint: discouraged parameter (link)