YOSEMITE NATIONAL PARK – More than a century after Hetch Hetchy Valley was flooded to supply water to San Francisco, a new analysis argues the original justification for the reservoir no longer exists — and that Yosemite National Park could be made whole again without risking water reliability for millions of Californians.
The January 2026 report, Restoring Hetch Hetchy: The Cherry Solution, outlines a detailed water supply alternative that would allow the O’Shaughnessy Dam reservoir to be emptied while maintaining full deliveries to the San Francisco Regional Water System.
Hetch Hetchy, once described as Yosemite Valley’s “sister,” was inundated following passage of the Raker Act in 1913, making it the only national park valley ever developed for the exclusive use of a single city. While controversial at the time — sparking one of the nation’s earliest conservation battles — the dam was approved to guarantee water security after San Francisco’s devastating 1906 earthquake and fire.
According to the new analysis, that century-old rationale no longer holds.
Water Demand Down, Storage Capacity Up
San Francisco’s regional water system now serves not only the city but also wholesale customers across San Mateo, Santa Clara, and Alameda counties, as well as Groveland in the Sierra foothills. Despite population growth, water use has dropped sharply.
From 2012 to 2022, average annual demand fell to about 220,000 acre-feet — a 19 percent reduction from the previous decade — due largely to conservation, efficiency standards, and changes in water use behavior
At the same time, San Francisco can store approximately 1.46 million acre-feet of water across nine reservoirs — more than six times its annual demand. Even without Hetch Hetchy Reservoir, the system would retain roughly five times annual demand in storage, the report states.
The “Cherry Solution”
The core proposal centers on reconfiguring how Tuolumne River water is conveyed to the Bay Area.
Under current operations, most water is diverted directly from Hetch Hetchy Reservoir. The Cherry Solution instead proposes allowing the Tuolumne River to flow naturally through Hetch Hetchy Valley, with water diverted at the valley’s outlet. During dry months, stored water from Cherry Reservoir — located just outside Yosemite National Park — would supplement supplies via a new conveyance known as the “Cherry Intertie.”
Cherry Reservoir, which is already connected to Lake Eleanor and operated as a single storage unit, would become the primary backup source when river flows are low. Modeling shows this intertie would be used mainly in late summer and fall, while spring snowmelt would provide most annual supply.
On average, about 122,000 acre-feet per year would come from natural river flows, with roughly 70,000 acre-feet supplied from Cherry Reservoir. Total deliveries to the Bay Area would remain unchanged.
Reliability Through Droughts
Using the Tuolumne River Equivalent Water Supply Simulation (TREWSSIM) model, the study evaluated system performance during historic droughts, including conditions similar to those ending in 1977 and 1992.
Even under those severe scenarios, minimum end-of-year storage would remain more than twice annual demand. The system would retain over two years’ worth of water in reserve, providing what the report describes as “high reliability” even without Hetch Hetchy Reservoir.
Importantly for Central Valley communities, the analysis concludes the proposal would not require changes to downstream facilities or water agreements. Releases supporting fisheries, hydropower generation, whitewater recreation, and water deliveries to the Turlock and Modesto Irrigation Districts would continue.
Local and Environmental Impacts
For residents of the Sierra and foothill communities, restoration would mean the return of a second world-class Yosemite valley, potentially easing crowding in Yosemite Valley while creating new recreation and tourism opportunities.
The Tuolumne River below Hetch Hetchy is already a popular destination for rafters and kayakers, and the plan assumes continued managed releases to support recreation. Natural river flows through the valley would also benefit wildlife habitat and ecosystem restoration.
The report notes that evaporative losses would decline without a large reservoir in the high country, resulting in a slight increase in downstream flows into Don Pedro Reservoir.
What About Power and Costs?
One remaining challenge is hydropower. Hetch Hetchy currently generates about 349 gigawatt-hours per year. While significant locally, the report notes this is a small fraction of statewide power generation and roughly half the energy lost when Klamath River dams were removed in 2024.
Options for addressing hydropower losses, dam removal or breaching, and funding mechanisms would need to be resolved in subsequent planning phases.
The report suggests that full removal of O’Shaughnessy Dam is not the only option. A partial breach allowing the river to pass could significantly reduce costs while restoring the valley’s natural character.
A Century-Old Debate, Renewed
Former Yosemite superintendents Robert Binnewies, B.J. Griffin, and David Mihalic argue in the report that retaining Hetch Hetchy Reservoir can no longer be justified.
“Since water supply for San Francisco is no longer dependent on storing water at Hetch Hetchy, the original justification for flooding such an iconic valley in a national park is no longer valid,” they write.
With water reliability addressed, the question now turns to political will.
Advocates say restoring Hetch Hetchy represents a once-in-a-generation opportunity — not just to undo a historic environmental loss, but to reimagine Yosemite for future generations while meeting modern water needs.
As the report concludes, it may finally be time to let the Tuolumne River run free again.
For more information on Restore Hetch Hetchy, visit their website at Restore Hetch Hetchy.
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