Lake Hollywood is a man-made reservoir built in 1924 to hold more than 2.5 billion gallons of water. The reservoir is part of the Owens River Aqueduct system. The Mulholland Dam was built by engineer William Mulholland who designed and built the system of aqueducts and reservoir providing Los Angeles with most of its drinking water. A small dam was subsequently built in the northern part of the lake to provide additional reservoir capacity. As a reservoir for drinking water, the lake is not open for swimming or boating and dogs are not allowed on the perimeter path. In 1974, the California State Department of Health Services directed the Department to further improve water quality and the protection of open distribution reservoirs. In addition to normal environmental exposures faced by open bodies of water, the Upper and Lower Hollywood reservoirs could be contaminated by surface runoff.
The initial plans, in 1988, proposed to install reservoir covers. To protest these plans, 15 community groups (including the HKCC) formed the Coalition to Preserve Open Reservoirs (CPOR). A mediation process in 1990 let to the current solution of buried water storage and a small filtration plant at the base of the dam.
The City of Los Angeles, Department of Water and Power (DWP), is moving toward completion of new water storage facilities next to the Upper and Lower HollywoodReservoirs. Two of the world’s largest underground tanks now store treated water, with new pipelines linking the tanks to the distribution system. Source http://www.hollywoodknolls.org/hollywood_reservoir.htm