Just as controversial is a huge plan pushed by Governor Brown to build two immense tunnels, at a cost of $15 billion, to move water from the upper reaches of the delta to the lower delta, bypassing some of the environmental problems. The goal is to create a more reliable system, but delta farm groups see the plan as an old-fashioned water grab by the southern part of the state.

On a boat ride in July through one of the delta’s channels, Anna Swenson, co-director of a community group called North Delta Cares, spoke of William Mulholland, the famed Los Angeles water boss who, in the early 20th century, purloined the water of the distant Owens Valley on behalf of his city.

“William Mulholland is in the grave, and so should his ideas be,” Ms. Swenson said. “The days when you could come up here and stick your straw in to satisfy your insatiable demands — those days are over.”

Elsewhere in the state, many farm groups support the tunnel plan, but others are wary, fearing they will be stuck with a large bill in exchange for minimal benefits. Mr. Brown has pledged to make water users, not taxpayers, pay for the tunnels, but it is not clear whether he will be able to pull together the financing.

The economics of the proposed dams are just as difficult. Farmers are not willing to pay the full costs, and a huge battle is expected over how to spend the $2.7 billion approved by California voters for water-storage projects.

“We should just be ruthless about this,” said Jay R. Lund, head of the Center for Watershed Sciences at the University of California, Davis. “It’s a straight-up calculation: What’s the benefit to the people of California compared to the costs? If you think your project is such a good project, prove it.”