The site itself is a naturally occurring valley near the small town of Maxwell, about 80 miles north of Sacramento. Once built, the reservoir will stretch 13 miles from north to south and 4 miles east to west, reaching about 260 feet deep at its lowest point. Two primary dams -- Sites Dam and Golden Gate Dam -- will hold water where the surrounding hills drop too low, joined by nine smaller saddle dams and dikes. The reservoir would become California's eighth largest, an enormous engineered lake sitting in terrain that has held nothing but grassland and cattle for generations. Water arrives through more than 100 miles of conveyance infrastructure, much of it already built: the Tehama-Colusa Canal carries Sacramento River water south from the Red Bluff Pumping Plant to Funks Reservoir, from which it would be pumped uphill into Sites through new pipelines and tunnels.

Sites Reservoir represents a different philosophy of water storage. Traditional California reservoirs -- Shasta, Oroville, Folsom -- dam major rivers and depend heavily on snowmelt. Sites catches rain. During wet winters, when the Sacramento River runs high and floodwater pours toward the Delta, diversions would pull surplus water into storage. Most filling would happen between December and March, after all senior water rights and environmental requirements are met. In dry years, that banked water flows back out. The maximum combined diversion capacity is about 4,200 cubic feet per second. Proponents argue this flexibility is exactly what California needs as climate change shifts precipitation from snow to rain and compresses the wet season into fiercer, shorter storms. The reservoir would complement Shasta Lake, potentially helping preserve cold water pools critical for endangered Sacramento River salmon.

In a first for California, the environment is planned to be the single largest beneficiary of water stored in Sites Reservoir. Under the terms of its Proposition 1 funding -- $816 million from the 2014 water bond -- the project must dedicate a significant share of its stored water to ecological purposes. Federal and state natural resource agencies would manage these environmental flows, directing water to support freshwater ecosystems in the Sacramento River and the Sacramento-San Joaquin Delta. The idea is that Sites could help maintain spawning habitat for chinook salmon, stabilize fall flows, and push back against saltwater intrusion in the Delta during dry periods. Whether this promise holds will depend on how competing demands are balanced in practice.

Not everyone is convinced. Environmental groups including the Natural Resources Defense Council and the Golden State Salmon Association argue the project will increase diversions from the Sacramento River and the Bay-Delta, harming salmon and other fish. Diversions could capture up to 60 percent of the river's flow at peak times. The reservoir's 14,000-acre surface would lose an estimated 30,000 acre-feet per year to evaporation alone, and construction would affect habitat for 23 sensitive, threatened, or endangered species. A 2023 report funded by Patagonia estimated the project would emit approximately 362,000 metric tons of CO2 equivalent per year over its assumed 100-year lifespan, with methane from decomposing organic matter as the primary driver. Tribes with cultural ties to the project area, conservation groups, and environmental justice advocates have raised objections throughout the process.

The project's journey from concept to construction reads like a history of California water politics itself. Proposed in the 1950s, it sat dormant through decades of competing priorities. Droughts in 1977-78, 2006-2010, and 2011-2017 revived interest each time. Preliminary studies ran from 1996 to 2014. The California Water Commission endorsed feasibility in December 2021. Governor Gavin Newsom certified the project in November 2023 under SB 149, streamlining judicial review. By July 2025, both state and federal wildlife agencies had approved key permits. The Sites Project Authority -- a coalition of about 30 public water agencies, irrigation districts, counties, and cities formed in 2010 -- selected Barnard Construction Company as the main contractor in January 2026. Operations are targeted to begin by 2034. If it works, Sites will prove that California can still build large-scale infrastructure. If it falls short of its water-yield projections, it will join a long list of expensive lessons.