Restore Yosemite? It can be done.

One hundred years ago this month, President Woodrow Wilson signed the Raker Act, which allowed San Francisco to build a dam in Yosemite National Park and convert the spectacular Hetch Hetchy Valley into a municipal reservoir.

As native Californians who have often visited Yosemite, we can think of no greater crime committed against the national parks. But it’s not too late to undo the damage. We should take the opportunity of this centennial to reform San Francisco’s water system and return Hetch Hetchy Valley to the American people.

Hetch Hetchy Valley was once home to a richly diverse ecosystem, surrounded by towering cliffs and waterfalls similar to those in neighboring Yosemite Valley. The Tuolumne River, the source of much of the Bay Area’s water, flowed through it unobstructed. Today, most of Yosemite National Park’s visitors crowd into Yosemite Valley, unaware of its submerged twin 15 miles to the north. Were the reservoir to be drained and Hetch Hetchy Valley restored, the world would rediscover one of America’s great natural treasures and tourist pressure on Yosemite Valley would be relieved.

The proposal to build a dam in Yosemite National Park was controversial. Naturalists, led by John Muir, and more than 200 newspaper editorials nationwide, opposed it. But San Francisco lobbyists were able to push it through Congress with the help of Interior Secretary Franklin Lane, San Francisco’s former city attorney.

Three years later, Congress responded to public disapproval over the flooding of Hetch Hetchy by passing the National Park Service Act to ensure that, going forward, national parks would be managed as a national system, not for local benefit. Subsequent proposals to build dams in Yellowstone and the Grand Canyon were defeated, and municipalities have not been allowed to appropriate land and other resources from national parks since then.

Extensive water supply development in California over the last century has been essential to support the state’s 38 million people and its world-class agricultural economy. However, such development has come at a sometimes unanticipated but nonetheless significant cost to vital natural resources.

Today we’re repairing environmental damage by removing dams and reducing diversions from our natural waterways. Los Angeles has reduced its diversion of the waters that feed Mono Lake, a vital bird sanctuary. And water agencies throughout the state, including virtually all of urban Southern California, have reduced diversions from the Sacramento-San Joaquin River Delta to protect and restore native fish populations.

California’s water agencies have also made significant investments to ensure reliable water supplies for their customers. They built Diamond Valley reservoir. They’ve cleaned up and learned to manage groundwater basins. They’ve built water-recycling facilities. They’ve developed relationships with agricultural agencies and committed to exchange and bank water. As a result of these programs and remarkable success in water conservation, our water supply is now more reliable and sustainable.

Last year, San Francisco voters were asked to approve the creation of a plan for similar water conservation reforms and for the restoration of Hetch Hetchy Valley. Though the plan would have been nonbinding, opponents suggested it would start the city on a path to less reliable and far more expensive water.

We believe the plan would have confirmed that reform is both possible and significantly cheaper than they claimed.

A well-financed negative campaign ensured the proposition’s defeat, in spite of numerous studies by government agencies, universities and independent groups that have concluded it would be possible for San Francisco to continue to obtain water from the Tuolumne River without storing it in Yosemite. Related reforms in the city’s water system, such as the development of additional infrastructure and supply, are also feasible.

It’s time for a bipartisan effort in Congress to consider amendments to the Raker Act that would stop the use of Hetch Hetchy Valley as a municipal reservoir. A first step would be to commission an independent analysis of practical alternatives and the actual cost of restoration and how that cost might be allocated. We also need to have a robust national dialogue about the value of restoring Hetch Hetchy Valley to the American people — as well as the economic benefits to California. Hetch Hetchy Valley should not be used as a water tank.

An amended Raker Act would not deprive San Francisco of its access to the Tuolumne River or of its other reservoirs and facilities in the river’s watershed. But it would require that Hetch Hetchy Valley be returned to the American people, making Yosemite National Park whole once again.

Former congressman Dan Lungren, a Republican, served as California attorney general from 1991 to 1999. John Van de Kamp, a Democrat, served as California attorney general from 1983 to 1991.