SACRAMENTO, Calif. — California’s ambitious $24 billion plan for ending the state’s water wars was unveiled Wednesday, but standing in its way are unanswered questions and hurdles that will take years to surmount if they can be at all.

With fanfare, Gov. Jerry Brown and Interior Secretary Ken Salazar touted a massive twin-tunnel system to carry water from the Sacramento-San Joaquin River Delta to vast farmlands and thirsty cities.

But critics say the proposal calls for costly construction before scientists determine the impacts on the fragile delta ecosystem, including its imperiled fish species.

Brown said the tunnels would guarantee a stable water supply for California while being able to withstand earthquakes and other threats. Construction alone would cost $14 billion.

“A healthy delta ecosystem and a reliable water supply are profoundly important to California’s future,” Brown said. “We know there are a couple big issues — earthquakes and climate change. And this facility is absolutely essential to deal with both of them.”

However, the proposal met stiff opposition from delta residents, environmental groups and Northern California legislators who say the tunnels could severely damage the delta ecosystem and agriculture-based economy.