As one of the wettest California winters in memory nears its end, the state’s major reservoirs are all essentially full or well above their historical average levels. It’s good news for everyone and everything that depends on water, especially after several years of reduced allocations for farmers and huge losses for salmon, which were frequently unable to spawn successfully for lack of cold water.

In spite of their replenished supplies, the glass is still half empty for many farmers and urban water districts. They feel the state should have had more, or higher, dams in place to bank away more of the precipitation that ran into the sea during the past few months.

“We could have captured that water if we had another reservoir,” says Nadine Bailey, chief operations officer with the Family Water Alliance, in the small Sacramento Valley town of Maxwell. “Right now, south of Lake Shasta, there’s nothing.”

Bailey’s organization stands in support of a controversial proposal to build a reservoir in the western Sacramento Valley. Named in its planning stages as Sites Reservoir, the artificial lake would hold as much as 1.8 million acre-feet (2.2 billion cubic meters) of water – half the capacity of Lake Oroville and a considerable addition to the state’s major reservoir storage capacity of 42 million acre-feet (52 billion cubic meters) of water. Its annual yield would be perhaps 500,000 acre-feet (617 million cubic meters), though possibly significantly less. The reservoir would not be located on a major river valley but, rather, in a relatively dry basin in the foothills of the Coast Range. This means it would not interfere directly with migrating fish, as do many other reservoirs, which prevent salmon from reaching their historical spawning grounds.

The idea would be to fill Sites Reservoir with water diverted from the Sacramento River during high-flow periods, building a supply that could be used later to provide for south-of-Delta farmers and cities. Proponents of the reservoir have also argued that it would help fish by improving flexibility in how and when water is released into the river. This could make flows more consistent through the year, they say.

But Gary Bobker, program director with the Bay Institute, isn’t convinced the reservoir would benefit the Bay-Delta ecosystem. Just filling it, he says, could prove problematic. The rapid, murky conditions in the Sacramento River created by seasonal rains provide a sort of smokescreen that helps juvenile salmon to dodge predators and to safely reach the ocean.

“Those high flows are critical for the Sacramento ecosystem,” Bobker says. “It’s the attenuation of those flows that has caused the collapse of the Bay-Delta ecosystem. So, filling Sites with winter-spring flows could be counterproductive to fishery restoration.”

While the Sacramento River runs, on average, five to six times higher in the winter and spring than it does in the summer, this doesn’t necessarily mean there is a surplus of water to be diverted, says Doug Obegi, senior attorney with the Natural Resources Defense Council (NRDC). He says filling the reservoir with water in the winter and spring might just worsen conditions that are already proving inadequate for struggling salmon populations. According to documents from the California Department of Water Resources, the Sacramento River’s long-term average flow is about 42,000 cubic feet (1,200 cubic meters) of water per second in January and March, with flows in February averaging more than 51,000 cubic feet (1,400 cubic meters). The Sites intake would, on average, take in about 12 percent of this volume – a diversion rate that Obegi says the salmon might be unable to tolerate.

“The modeling shows that this project could significantly reduce flows through the Delta,” says Obegi, who adds that the NRDC hasn’t yet taken a formal stance for or against the proposed reservoir.

To fund Sites Reservoir, which could cost anywhere from $3 billion to $4.4 billion to construct, the state could dip into the cash pool of Proposition 1, the $7.5 billion water bond approved by voters in 2014. Prop 1 specifically offers $2.7 billion for water storage projects, and it could be used to cover up to half Sites Reservoir’s price tag. To receive funding from the water bond, though, the project would need to offer a clear public benefit, including a boon to aquatic ecosystems – and it isn’t yet clear that it will. After all, few dams, if any, have been beneficial to native fishes in California. The Friant Dam, for example, extinguished the once enormous population of Chinook salmon that spawned annually in the San Joaquin River. Shasta and Oroville dams also seriously dented salmon numbers in the Sacramento system.

For human users of water, though, the Sites Reservoir offers obvious benefits. That’s why the Metropolitan Water District of Southern California, which uses Northern California water to serve millions in the Los Angeles area, has offered to help pay for the Sites project to the tune of $1.5 million for the development and planning stages.

Randall Neudeck, the Metropolitan Water District’s program manager on Bay-Delta initiatives, says Sites Reservoir is necessary as “another tool in the toolbox” to help society adapt to a changing climate and increasing demands on the state’s water supply.

“Sites will improve our ability to capture surplus flows and use them both for environmental needs and to bolster our water supply,” Neudeck says. He says a significant surplus of water could be captured and diverted over many years without harming the environment, though watchdog organizations have argued that the minimum sustainable flows defined by state agencies are already insufficient to protect fish populations.

The environmental community remains uncertain how the Sites project could impact natural resources. If the water stored in the reservoir is used only to help water managers meet existing allocations, Sites could be a boon to all Californians as well as to fish. On the other hand, Sites could further imperil strained salmon populations if the reservoir is ultimately used to create new water dependence, for example with more orchards in the San Joaquin Valley.

John McManus of the Golden Gate Salmon Association says it’s too early for his group to formally support or oppose the project.

“But salmon fishermen notice with suspicion that the Metropolitan Water District has made an investment and expects to eventually get more Northern California water out of the deal,” McManus says.

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