SACRAMENTO  (AP) — Gov. Jerry Brown took a sarcastic approach to critics of his $15 billion twin tunnel plan Wednesday, saying unless they have invested a million hours working on the problem as his staff has, they should “shut up.”

The Democratic governor made the comments while speaking to officials from California water agencies, who have widely varying views on the project. He said he asked his “water man” how many hours have been invested on efforts to build tunnels to send water around the Sacramento-San Joaquin Delta, and the answer was 1 million.

“Until you put a million hours into it, shut up,” Brown said to laughter. “You don’t know what the hell you’re talking about.”

Brown said the problem of how to convey water from Northern California to Southern California has confounded governors for 50 years and is so complex that the latest plan for how to do it runs tens of thousands of pages.

“Folks, it’s complicated, and on this subject we do want to be thoughtful,” he told the Association of California Water Agencies.

Critics of the project said Brown’s comments reflect his refusal to listen to scientists, economists, editorials and thousands of critical comments submitted to the state.

The real Delta experts are those who live and work in the Delta, said Barbara Barrigan-Parrilla, executive director of Restore the Delta, which opposes the tunnels.

“We won’t go away. We will not shut up,” she said. “We can’t stand by and watch a project move forward that’s going to destroy the most important estuary on the West Coast of the Americas or completely destroy California’s largest watershed.”

A spokesman for the governor, Evan Westrup, said in an email later, “We listen to critics and supporters alike.”

“That’s a big part of the million hours we’ve put into this project and we’ll keep the same open spirit in the coming months,” he said.

Under development for eight years, the Bay Delta Conservation Plan calls for building two underground tunnels, 40 feet across and 30 miles long, to send water from the Sacramento River around the Delta. The water currently irrigates 3 million acres of farmland in the Central Valley and serves 25 million people as far south as San Diego.

The plan is designed to stabilize water supplies for cities and farms south of the Delta. But it has drawn strong opposition from Delta farmers and environmentalists, who contend that the tunnels will allow salt water from San Francisco Bay to degrade the Delta’s water quality and damage habitat for endangered salmon and tiny delta smelt.