What was once described as “Yosemite’s sister valley,” Hetch Hetchy was an expanse surrounded by granite walls, full of life within its meadows, and picturesque waterfalls. Early visitors, in their accounts of the valley, described it in much the same grandeur as the Yosemite Valley.

However, today that valley lies beneath the waters of a reservoir, since it was flooded more than a century ago to meet the water needs of the San Francisco Bay Area. The debate about whether to restore Hetch Hetchy to its natural state has never ceased, and it raises a larger question about how we, as Californians, value our natural spaces and National Parks.

The story begins after the 1906 earthquake and the subsequent fires that would devastate San Francisco. City leaders argued that access to a reliable water supply was essential for the city, and their solution was to dam the Tuolumne River at Hetch Hetchy Valley, located within Yosemite National Park.

In 1913, Congress passed the Raker Act, which authorized the construction of the O’Shaughnessy Dam, despite heavy opposition from naturalist and parks visionary John Muir, as well as the Sierra Club, which Muir founded. For Muir, the decision to flood the valley was a tragic one, and seen as a violation of a national heritage meant to be preserved for future generations.

Muir was quoted as saying, “Dam Hetch Hetchy! As well dam for water-tanks the people’s cathedrals and churches, for no holier temple has ever been consecrated by the heart of man.” The fight over Hetch Hetchy would become one of our nation’s first debates about the conservation and preservation of our lands.

Today, this reservoir continues to provide some of the cleanest water in our country and also generates hydroelectric power for the San Francisco Bay Area. Explorers can still walk on the shoreline here, surrounded by massive granite cliffs, which very much hint at the lost beauty of the valley.

Yet for most tourists and residents of California alike, Hetch Hetchy remains far less known than Yosemite, even though it holds immense importance — namely, as the source of water for many  in the Bay Area.

Calls for the valley’s restoration have persisted to our current day. Supporters of restoration argue that draining the reservoir would restore the meadows and forests within a few years, as well as attract millions of tourists and locals back into the valley. Besides the ecological reasoning, they also point to the great symbolism of the place: restoring Hetch Hetchy to its former glory would fulfill John Muir’s vision of what could have been, as well as honor the ideals of what our National Parks system should have been. Proponents cite other examples of restoration, like the Elwha River in Washington state, where the removal of a dam led to a rapid recovery of its ecosystem.

Zan Rubin, a hydrologist and geomorphologist based in Berkeley, said, “We’ve seen a few places where fish, forests, and coastlines can recover quickly. The Elwha and other removals have shown us it is definitely possible.”

“But every river and reservoir is unique,” he added, “and Hetch Hetchy is more critical to California’s water system, which makes it a bigger challenge.”

Opponents of the restoration, meanwhile, argue that Hetch Hetchy is far too important a resource to simply get rid of. About 7.5 million people in the Bay Area rely on the reservoir as their primary source of water, and its hydroelectric power helps California meet its goal of having clean energy sources.

The incredible financial costs of dismantling the dam and building replacement infrastructure would likely amount to billions of dollars. Thus, restoration opponents say the incredible usefulness and practicality of the reservoir, to fuel the entire Bay Area’s water needs, far outweigh the benefits of restoring it to its natural state.

As this tug-of-war continues, advocacy groups are keeping John Muir’s ideas alive through different lawsuits, ballot measures, and campaigns to spread awareness about the valley and its history. Officials across the San Francisco region remain divided, with some of them dismissing the restoration project as unrealistic.

But the discussion represents more than just a regional dispute. Hetch Hetchy has become a symbol for the American struggle to find balance for our human needs along with our environmental ideals. At the core of the conflict is a question: can, or should, a valley that was once sacrificed to progress be returned to its natural state?