The Hetch Hetchy Reservoir is a reservoir in Yosemite National Park in California. Following the 1906 earthquake in San Francisco, residents needed a source of clean water. While the project was strongly opposed by environmentalists, in 1913 President Woodrow Wilson signed the Raker Act, which allowed the dam to be built in 1923 along the Tuolumne River. The reservoir holds over 117 billion gallons of water and serves as a water supply for more than 30 cities in the area.
Many studies through the years have focused on wanting to restore the Hetch Hetchy Valley to its natural state and establish reforestation and habitats. Restoration of the Valley by removing the dam is on the California state November ballot. If restoration passes, plans will be made for water conservation practices in the cities affected, and pre-dam conditions will be restored.
The USGS archive of satellite imagery has proven useful by providing a historical view of the area. Landsat imagery from 1985 and 2011 show the areas and water fluctuations of Hetch Hetchy Reservoir (long water body on the right side of the image), along with Cherry Lake (far left) and Lake Eleanor (central), which are also reservoirs for the Hetch Hetchy Reservoir System. The light tones along the shorelines in the 1985 imagery show diminished water levels that year.