With fanfare, Gov. Jerry Brown and Interior Secretary Ken Salazar touted a massive twin-tunnel system to carry water from the Sacramento-San Joaquin River Delta to vast farmlands and thirsty cities.
But critics say the proposal calls for costly construction before scientists determine the impacts on the fragile delta ecosystem, including its imperiled fish species.
Brown said the tunnels would guarantee a stable water supply for California while being able to withstand earthquakes and other threats. Construction alone would cost $14 billion.
"A healthy delta ecosystem and a reliable water supply are profoundly important to California's future," Brown said. "We know there are a couple big issues earthquakes and climate change. And this facility is absolutely essential to deal with both of them."
However, the proposal met stiff opposition from delta residents, environmental groups and Northern California legislators who say the tunnels could severely damage the delta ecosystem and agriculture-based economy.
During the announcement by Brown and Salazar, dozens of opponents gathered on the Capitol steps and carried signs reading "kill the canal" and "the tunnel will suck California dry."
Opponents say it's unacceptable to proceed without knowing upfront how construction would impact already imperiled fish species such as salmon and smelt. Others said the project could be beneficial to fish but only if studies are done before construction.
"We're really concerned they want to divert too much water south without figuring out the impact on salmon," said Victor Gonella, president of Golden Gate Salmon Association. "There's no hard science on how much is the right amount of water to be pumped, when it can be taken and how. Heck, we're going to build this and whatever we ruin, we'll figure out how to fix later."
Officials said an environmental impact report on the proposal would begin in the fall. And scientific studies will accompany construction over the next 10-15 years.
Construction costs would be covered by water users, and taxpayers would bear an additional $10 billion cost of habitat restoration that involves creating 100,000 acres in floodplains and making other improvements. A water bond that could provide some money for restoration is set to appear on the November 2014 ballot.
Officials said they will continue to weigh different alternatives and project sizes. Permits are expected to be issued next year and construction could start in two to three years.
The delta, an inland estuary where hundreds of species live, is the hub of California's water delivery system. The Sacramento and San Joaquin rivers drain into the delta, and the state and federal governments run massive pumps that siphon drinking and irrigation water for use by more than 25 million Californians and farms in the Central Valley that produce half the nation's fruits and vegetables.
The current distribution system falls short of providing all the water needed by cities and farms. Supply was tightened even more a decade ago when major declines in the once-abundant fish populations spurred regulations that curtailed delta pumping and water deliveries.
Farmers and urban water users have long called for a new water system, but Brown faced stiff opposition in 1982 when he proposed a peripheral canal during his previous time as governor that would carry water around the delta. Voters rejected that plan, branding it a water grab by Southern California cities.
The current proposal two tunnels, each larger than 33 feet in diameter would have the capacity to divert about 67,500 gallons of water a second, a pace that would fill six Olympic-sized swimming pools every minute.
Officials said they want to build it even larger to help water move by force of gravity, reducing energy use. They did not say how much water will be diverted through the tunnels each year.
The tunnels would change the point of water diversion from the south end of the delta to the north end below Freeport. Salazar expects that to lessen the impact of giant pumps now blamed for killing massive numbers of salmon, sturgeon and other species.
Once water reaches a pumping station in Tracy, it would be ferried through existing canals to farms in the Central Valley and cities such as San Diego and Los Angeles.
Still, officials couldn't guarantee that they could fully balance the needs of water users against those of the ailing ecosystem.
"We have so much more science. We're a lot more sensitive to the species," Brown said. "We're going to do as much as we can ... to protect these environmental interests. Is there absolute certitude? No."
Precisely how much water is diverted will depend on the health of fish species, the officials said.
Rep. John Garamendi, D-Walnut Grove, said the tunnel proposal put "plumbing before policy" and would devastate the delta to get water to Southern California farmers and cities.
"This proposal does not develop one gallon of new water, but it delivers precious water that the fish need to the tunnel so it can go south," he told the crowd at the Capitol.
"It is the pumping from the Delta that has largely destroyed the Delta," he added later.
Wozniacka reported from Fresno, Calif.