The primary purpose is to supply drinking water to the San Francisco Bay Area. It is one of nine reservoirs in San Francisco's system and holds about 25% of its overall storage capacity. The water is transported from the reservoir by the Hetch Hetchy Aqueduct. Hydroelectricity is also produced by Kirkwood Powerhouse and Moccasin Powerhouse, which have a capacity of 118 and 100 megawatts, respectively. Because Hetch Hetchy is a municipal water supply and its water is not filtered, swimming and boating are prohibited. Fishing is permitted only from the lake shore.