The board of the Metropolitan Water District of Southern California voted Tuesday to support Gov. Jerry Brown’s much-debated plan to build two giant tunnels beneath the Sacramento-San Joaquin River Delta to shore up the state’s water supplies.

The Los Angeles-based MWD, Southern California’s water wholesaler, agreed to commit $4.3 billion toward the $17 billion California WaterFix project, despite claims by critics that the project will drive up residents’ water bills as high as $16 a month.

Approval of the project ultimately lies with the state’s water boards, and if enough water districts do not vote to fund the tunnels, they will not be built.

The vote by the WMD was considered by some observers to be a make-or- break decision on the tunnels, as another major water agency, the Westlands Water District, last month rejected helping to pay for the project.

Some environmental groups are opposed to the project, including the Sierra Club and Food and Water Watch, which argue the tunnels could be harmful to the environment and not worth the cost.

Brown has argued the tunnels will help the environment by protecting fish and also securing a more reliable delivery system for the water.

— From Staff and Wire Reports

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