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Bay Area Officials Celebrate the Centennial of O'Shaughnessy Dam

Hetch Hetchy Centennial

Mayor’s Office of Communications

Wednesday, May 3, 2023

Bay Area Officials Celebrate the Centennial of O'Shaughnessy Dam

The keystone of the Hetch Hetchy Regional Water System that provides high-quality, reliable water turns 100

SAN FRANCISCO – Mayor London N. Breed and Bay Area and federal officials joined the San Francisco Public Utilities Commission (SFPUC) to commemorate the centennial of the O’Shaughnessy Dam construction, which was completed in 1923. The dam, a testament to vision, ingenuity, and sustainability, provides high-quality drinking water to 2.7 million residents and thousands of businesses in four Bay Area counties.  

“Today, we not only celebrate O’Shaughnessy Dam and the system that it anchors as engineering marvels, but we also recognize those who had the foresight and ingenuity to build them,” said Mayor Breed. “We are committed to continue to be environmentally conscious and good stewards of our water resources so we can serve the people of San Francisco, the Bay Area, and California for generations to come.”    

Hetch Hetchy Plaque

“For 100 years, the O’Shaughnessy Dam and Hetch Hetchy Reservoir have supplied the Bay Area with clean drinking water and energy,” said Senator Dianne Feinstein. “The dam and reservoir are critical to our state’s water infrastructure and clean energy goals, so I thank everyone who has helped maintain and operate them.”  

“The Hetch Hetchy Regional Water System has been a proven model of sustainability, and O’Shaughnessy Dam has been the keystone of that system for 100 years,” said SFPUC General Manager Dennis Herrera. “The system and the protected Tuolumne River watershed within Yosemite National Park provide clean drinking water for 2.7 million people using the most sustainable force around: gravity. It is also a clean energy trailblazer, generating 100% greenhouse-gas-free electricity that powers an airport, transit system, schools, libraries, and many other parts of everyday life in our world-renowned city. Without a reliable source of clean drinking water, San Francisco doesn’t become a major city. Without this system, the Bay Area as we know it doesn’t exist. That’s why we work continuously to support proactive environmental stewardship with the National Park Service and are making continued infrastructure investments to ensure the system serves the people for another 100 years.”  

100 Years of Sustainability, from Source to Tap 

O’Shaughnessy Dam and the Hetch Hetchy Regional Water System have been sustainable before it became a buzzword. The system delivers drinking water to the Bay Area using only the power of gravity. The system also generates greenhouse-gas-free hydropower to support San Francisco. The Tuolumne River Watershed is so well protected, and the system so efficient and effective that it is one of only a few water systems in the nation with a filtration exemption. The water from Hetch Hetchy Reservoir is so clean it does not have to be filtered or requires a chemical- and energy-intensive filtering process.  

Held by O’Shaughnessy Dam, water sourced from the Hetch Hetchy Reservoir travels through hydroelectric powerhouses before entering the San Joaquin Pipelines, the Tesla Ultraviolet Treatment Facility, and the Coast Range Tunnel on its journey to the Bay Area. Due to this design, the SFPUC generates clean electricity for San Francisco municipal services including Muni, Zuckerberg San Francisco General Hospital, and San Francisco International Airport, as well as large developments such as the Salesforce Transit Center. Currently, the Hetch Hetchy Power system provides nearly 20% of the electricity used in San Francisco. 

"The availability of high-quality water from the Hetch Hetchy Regional Water System has been a driving force behind the thriving Bay Area,” said Nick Josefowitz, Chief Policy Officer at SPUR, the Bay Area planning and urban research association. “Since the system was constructed, we've seen the Bay Area transform into an economic powerhouse and global center for innovation. We've also developed a deeper appreciation for social equity, ecosystem health, and our vulnerability to climate change. We applaud the SFPUC's international leadership on climate resilience, alternative and recycled water use, and water conservation. As we celebrate the O’Shaughnessy Dam’s centennial, we invite the Bay Area to recognize the essential role of clean, reliable water in shaping the region we love, and to consider how we can continue to adapt to modern values and a changing climate." 

O'Shaughnessy Dam History 

The story of the Hetch Hetchy Reservoir dates to the early 20th century when San Francisco faced a pressing need for a reliable water supply. The 1906 earthquake and subsequent fire exposed the vulnerability of the city's existing water infrastructure. City leaders, including engineer Michael M. O'Shaughnessy, seized the opportunity to pursue the creation of a water system that would not only meet the needs of a growing city, but also handle future growth and challenges. 

In 1913, President Woodrow Wilson signed the Raker Act into law, granting San Francisco the rights to dam the Tuolumne River and build the Hetch Hetchy water system. The dam's location -on federal lands protected in perpetuity - was chosen for its naturally clean water supply untouched by construction, commercial development, or proximity to industry.  

The dam's construction began in 1914 under O'Shaughnessy’s leadership and supervision and was completed nearly a decade later, in 1923. The project faced numerous obstacles, including legal challenges, engineering feats, and issues related to building in remote areas.  

An Environmental Protection Partnership for Generations 

The construction of O’Shaughnessy Dam has forged a strong collaboration between the SFPUC and Yosemite National Park. Both agencies share a commitment to protecting the Tuolumne River's natural ecosystem and its majestic surroundings for current and future generations. The SFPUC works closely with Yosemite National Park to study and proactively protect the Tuolumne River watershed, including annual funding of more than $8 million a year for various projects and initiatives, ranging from trail maintenance and wilderness education to fire protection planning. 

This ongoing collaboration highlights the importance of protecting and preserving the unique environment that allows the Hetch Hetchy system to thrive, while respecting the delicate balance between human needs and environmental conservation.  

An Engineering Marvel with No End Date 

The dam's design and construction showcase the determination of the visionaries who built it.  

Today, San Francisco’s water supply comes from multiple protected sources managed by the SFPUC. These sources include surface water stored in reservoirs located in the Sierra Nevada, Alameda County and San Mateo County, and groundwater supplies stored in a deep aquifer located in San Francisco and San Mateo counties. These sources are diverse in both the origin of the supply – snowmelt, rainfall and recharge of groundwater – and their location within the system.  

Maintaining this variety is an important component of near- and long-term water management strategy. A diverse mix of sources protects customers from potential disruptions due to emergencies or natural disasters, provides resiliency during periods of drought, and helps ensure a long-term, sustainable water supply as we address issues such as climate uncertainty, regulatory changes, and population growth. 

The SFPUC also maintains a robust dam safety monitoring and maintenance program to ensure the integrity of the Hetch Hetchy system and to protect the public. 

Continued Investments in Our Future 

The City remains committed to making critical investments in the Hetch Hetchy Regional Water System. Through the Water System Improvement Program, a $4.8 billion, multi-year capital initiative to repair, replace, and seismically upgrade crucial portions of the system, the SFPUC is ensuring clean, high-quality and reliable water service for future generations.  

The program consists of 87 projects - 35 local projects located within San Francisco and 52 regional projects, spread over seven counties from the Sierra foothills to San Francisco.  

The San Francisco portion of the program was 100% complete as of October 2020. The regional portion is approximately 99% complete. The overall Water System Improvement Program is slated to be completed by summer 2023.  

For more information on the Hetch Hetchy Regional Water System, click here