Watershed Keeper Mike Fong,walks under one of the needle valves used to release water from the dam. Valves built in 1934 coild use new seals inside. The Hetch Hetchy Dam in the Yosemite Valley, receives the bulk of it's water from the sierra snow pack miles above the reservoir. Wapama Falls spills into the basin. City of San Francisco, Hetch Hetchy Water system that supplies the entire city. by Michael Macor/The Chronicle Photo: MICHAEL MACOR
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