SACRAMENTO  (AP) — Gov. Jerry Brown is rethinking a major component of the state’s proposed $25 billion twin-tunnel water project, a newspaper reported.

The governor is proposing to drop a 50-year guarantee to restore the environment in the Sacramento-San Joaquin Delta as part of the twin-tunnel plan, the San Jose Mercury News reported. The goal is to restore salmon and other endangered species in the Delta.

The change comes after biologists at the U.S. Fish and Wildlife Service and other federal agencies told the state they won’t issue permits for the environmental plan because the state cannot prove it will restore salmon, smelt, sturgeon and other wildlife, the Mercury News reported.

The newspaper said loss of the 50-year guarantee could make it harder for Brown to win backing for the project from people in Northern California and water districts that the state is relying on to pick up the tab for the tunnels.

“I think that it would be a concern for the public if the twin tunnels project would move ahead without the long-term environmental protections in place,” said Barbara Keegan, a board member of the Santa Clara Valley Water District.

Richard Stapler, a spokesman for the California Natural Resources Agency, said the state was still committed to restoring endangered salmon and other species in the Delta, and the goal would remain part of the project despite loss of the 50-year guarantee. The state plans to release an addendum to the project’s environmental impact report that reflects the proposed change in the next few months.

“We remain deeply committed to achieving the dual goals of water supply reliability and ecosystem restoration,” he said.

Brown said Saturday the change was a “technical point” based on concerns that the scientific predictions behind the 50-year permit might need to be modified down the line.

The tunnels are designed to send water around the Delta to Central Valley farms and Southern California cities. The proposed pair of 40-foot-wide tunnels would reach depths of 150 feet below ground and run for 30 miles bypassing the Delta. Some 25 million Californians rely on the Delta, say state officials, noting it plays a vital role in the state economy.

Supporters say the tunnels would increase the reliability of the water supply by reducing reliance on large pumps that can kill fish.

Environmentalists, delta farmers and the fishing industry want to block the project, saying the tunnels would further harm the delta and its water quality.

Water districts were counting on the 50-year environmental restoration guarantee to protect them from decisions by the federal government that have limited pumping in recent years to protect endangered fish, the Mercury News reported.

Removal of the 50-year environmental restoration guarantee could also give more ammunition to environmentalists, who would find it easier to attack the plan as a water grab by Southern California, the Mercury News reported. That would make the project less popular with Northern California residents.