A judge on Thursday dismissed a lawsuit seeking to force the city of San Francisco to drain Hetch Hetchy Reservoir, a key part of the water system for 2.6 million residents of Bay Area cities stretching from Hayward to San Jose to San Francisco.

The ruling, by Tuolumne County Superior Court Judge Kevin Seibert, is the latest setback for Restore Hetch Hetchy, an Oakland-based group that says construction of the reservoir in Yosemite National Park 93 years ago was a grievous crime against nature that can be undone, restoring the submerged valley.

The organization, which has the support of actor Harrison Ford, three former Yosemite park superintendents, the Sierra Club and the Environmental Defense Fund, also lost a ballot measure in a landslide in 2012, when 77 percent of San Francisco voters rejected studying the feasibility of draining the reservoir.

“Draining Hetch Hetchy Reservoir is a terrible idea that an overwhelming majority of San Francisco voters rejected in 2012,” San Francisco City Attorney Dennis Herrera said in a statement. “This lawsuit was a bid by the very same advocates to accomplish in a Tuolumne County courthouse what they couldn’t in a San Francisco election.”

Supporters say that water that flows from the Sierra Nevada, through the Tuolumne River and into the reservoir can be stored in Cherry Reservoir, Don Pedro Reservoir and others downstream. As a result, the suit contends, San Francisco, which owns the Hetch Hetchy water system, is not following a key provision of the state constitution requiring that water in California “be put to beneficial use to the fullest extent possible” and be used in “reasonable” ways.

“We intend to capture every drop of Tuolumne River water we’re capturing now,” said Spreck Rosekrans, executive director of Restore Hetch Hetchy. “People would still get the same amount of water; it would just be stored in other reservoirs.”

The judge rejected the group’s challenge, saying that the environmentalists’ arguments were pre-empted by federal law — specifically the Raker Act, a 1913 law signed by President Woodrow Wilson over the objections of Sierra Club founder John Muir. It authorized construction of O’Shaughnessy Dam, submerging the spectacularly scenic Hetch Hetchy Valley under 300 feet of water.

Further, the judge noted in granting San Francisco’s motion to dismiss the case that the provision of the California Constitution that the environmentalists used to support their arguments, Article 10, Section 2, was not passed until 1928 — five years after the dam was built.

Rosekrans said his group’s efforts will go on.

“We think the court got it wrong,” he said, “and we intend to appeal.”

Paul Rogers covers resources and environmental issues. Contact him at 408-920-5045. Follow him at Twitter.com/PaulRogersSJMN