California promises to restore 32,000 hectares of the depleted Sacramento-San Joaquin river delta as part of a project to send fresh water from mountain streams in the north to the parched south.
The US$16 billion plan comes as the state struggles in what is shaping up as its driest year on record, with some farmers and urban water districts promised just 5 per cent of the water that they had requested for next year.
The ambitious programme would divert water from the Sacramento River above the delta, sending it through massive underground tunnels to provide for two-thirds of the state's population, from San Jose to San Diego, and thousands of farms.
"This is a rational, balanced plan to help meet the needs of all Californians for generations to come," California natural resources chief John Laird said.
If the plan is put into place, it would change the state's system for water delivery from the region, which now involves pumping it from the delta itself in a practice that harms the fragile ecosystem and leaves farmers and residents with widely varying amounts of water from year to year. Under the new proposal, about half the water would be pumped from above the delta and sent through the tunnels.
The state aims to protect 56 plant and animal species as part of its plan. Habitat for the plants and animals declined after years of pumping water from the delta for use in drier regions.
Environmentalists complain that construction of the two tunnels would cause years of disruption while still failing to protect the delta.