In theory, the tunnels, an updated version of the peripheral canal Mr. Brown championed unsuccessfully in the 1980s, could increase the water available for export and reduce the saltiness, by drawing from the cleaner Sacramento instead of solely from the San Joaquin. The plan could also help keep delta smelt and other fish from being pulled into the pumps.

But Ms. Hildebrand and other farmers in the delta oppose the $15 billion plan, saying that they doubt it would solve the problem of saltwater intrusion.

“You’re just transferring the same impact from one area to another,” said Russell E. van Löben Sels, whose family has been farming in the delta since the 1870s.

Environmental groups are also leery.

“I don’t think anybody disputes that they could be operated in a way that is good for the environment,” said Jay Ziegler, director of external affairs and policy for the Sacramento office of the Nature Conservancy, which owns land in the northeastern part of the region. “But the devil is in the details.”

Like others, he believes something must be done if the delta is to survive the drought and continue as both a natural habitat and a water supply — eventually, the lack of freshwater could increase saltiness in the estuary to the point that pumping out water for exports becomes impossible, a dire situation even for those who care little about fish.

But is the solution to a problem caused by human engineering more engineering?

“I think we’re all skeptical about that,” Mr. Ziegler said.

More plausible, in a state that is likely to become drier over the decades, is a scaling back of expectations, an acknowledgment that all sides may have to give up something — not every farm will have water, not every shower will be long, not every species will thrive.

Said Mr. Isenberg, of the stewardship council: “It’s a much more adult discussion to acknowledge that the problems are serious, the solutions are tentative, and it’s going to take a lot of money.”