California's largest water agency on Tuesday approved a nearly $11 billion plan to help fund two enormous tunnels, breathing new life into Gov. Jerry Brown's ambitious and controversial plan to remake the state's water system.

The board of the Metropolitan Water District of Southern California (MWD) voted in favor of bearing most of the cost of the twin-tunnel project that would modernize the aging infrastructure that delivers water from the Sacramento-San Joaquin Delta.

"This is a historic decision that is good for California – our people, our farms, and our natural environment," Governor Brown said in a statement praising the decision to revive the plan.

He has supported the project for years and very nearly saw it fall apart with less than a year left in his administration after some water districts balked at the nearly $17 billion total cost.

Brown wants California water agencies to pay to build two, 35-mile-long tunnels to divert part of the state's largest river, the Sacramento, to supply water to the San Francisco Bay Area, the agricultural San Joaquin Valley, and southern California.

The MWD vote, which secures about $10.8 billion, does not guarantee the tunnels will be built. The project still requires multiple permits and faces legal challenges by opponents who consider it too expensive and dangerous. Environmentalists who fear negative effects on fish, wildlife, and water quality are pushing for more sustainable developments such as recycling and storm water capture.

The tunnels will be "litigated for years to come," predicted Kathryn Phillips, director of Sierra Club California.

Golden Gate Salmon Association president John McManus said his group and its allies "are already in court challenging this project because federal fish experts have found the twin tunnels will be a disaster for salmon."

MWD board chairman Randy Record said he was moved by board members who argued monumental upgrades are necessary to avoid the havoc unleashed by hurricanes on aging water systems in Texas and Louisiana. Supporters say the delta's delivery system is outdated and increasingly vulnerable to earthquakes, flooding, saltwater intrusion, sea level rise, and environmental degradation.

"We need to move forward now to make sure we don't have a natural disaster that impacts our water supply," Mr. Record said.

Brown and other project supporters say the two tunnels will modernize California's outdated north-south delivery system, where pumps and overall water withdrawals are blamed for the steady dwindling of native fish and other wildlife that depend on delta water.

The original funding blueprint collapsed last year when districts in the San Joaquin Valley backed out of an agreement to pay for half the twin-tunnels project.

In February Brown reluctantly agreed to trim the project down from two tunnels to one and build it in stages, in an effort to help line up enough money and ease environmental concerns. The MWD could have decided to approve the cheaper single-tunnel plan with $5.2 billion in funding but instead opted to pay for the full project.

The MWD has been the steadiest long-term supporter of either one tunnel or two – saying each project would help secure water for its millions of urban customers.

Tuesday's vote pitted MWD's two biggest members, the city of Los Angeles and the San Diego County Water Authority, against its third-largest member, the Municipal Water District of Orange County – one of the agencies that pushed to get the two-tunnel proposal back on the agenda.

Los Angeles has the biggest vote under MWD's system, which weighs the votes of member agencies according to assessed property values in their service areas.

Opponents rallied before the vote to urge the board to reject both tunnel plans, which they said will raise water bills and property taxes without delivering any water or economic benefits to southern California residents.

MWD officials said the agency's increased investment in the project is expected to cost the average southern California household up to $4.80 per month in increased water bills. Critics have estimated a much higher impact, suggesting monthly bills for Los Angeles residents could jump by as much as $16 per month.

Environmental groups have opposed the original twin-tunnel project, fearing southern California water agencies would use the tunnels to drain too much water from the Sacramento River, above its delta with the San Joaquin River.

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The Sacramento is the state's biggest river and a vital supplier of fresh water to the San Francisco Bay, part of the largest estuary on the West Coast of the Americas.

This story was reported by The Associated Press.