Perhaps the most famously controversial dam in the United States is the one San Francisco built on the Tuolumne River in the Hetch Hetchy Valley of the Sierra Nevada to supply the city with fresh water.
The O'Shaughnessy Dam was completed in 1923. (Downstream from this dam are the Kirkwood, Moccasin, and Holm hydropower facilities.) John Muir and other early environmentalists vigorously opposed the plan to flood the Yosemite Valley. Environmental groups are currently arguing for the removal of the dam.