Hell Hole reservoir is an artificial, crescent-shaped lake in the Sierra Nevada mountain range 10 miles (16 km) west of Lake Tahoe in California. The lake is about 3.5 miles (5.6 km) long when at full capacity.The lake was created in 1966 with the completion of Lower Hell Hole Dam across the Rubicon River, which is a major tributary of the Middle Fork of the American River. Hell Hole is named for a deep canyon which is now under the waters of the lake.
Lower Hell Hole Dam (its official name) is operated by the Placer County Water Agency, a powerful political force in the region. The agency controls two dams in the Eldorado and Tahoe national forests. The water agency gained its power from financing approved by Placer County voters in 1961.
Proposals for the dam date to 1958. In 1964 the first Hell Hole dam was completed. Placer County sought drinking water supplies to fuel growth of its communities in the Sacramento Valley. The gold-rush-era town of Auburn is in Placer County as is the suburban community of Roseville. The agency also sought to generate hydroelectric power to finance its ability to deliver the water to users.
Today, the lake offers modern facilities to aid in waterborne recreation. The remoteness of the lake limits the number of visitors, so the lake is seldom crowded even during the height of the summer season. Most boating activity is limited to small powered fishing skiffs, canoes and kayaks. Afternoon high winds can make boating precarious.
The lake also features many small granitic islands that expand and contract with the level of the lake. Hell Hole typically has its highest level of water in May and lowers gradually through the summer and fall. The forest service maintains visitor services from May 15 through September 15. The lake is accessible until snow makes roads to the area impassable. In 1984, the federally protected Granite Chief Wilderness was created by the United States Congress after a long advocacy campaign by the Sierra Club, a conservation organization.
The construction of the present Hell Hole Dam also changed the course of the Rubicon River. The pre-dam river channel wended its way several miles to its confluence with the Middle Fork of the American River near Ralston Afterbay. Now, In addition to releases from Hell Hole down the pre-dam path, water is diverted through a pipeline to Middle Fork Powerhouse (AKA Stephenson Powerhouse) where it flows into Interbay Reservoir. From here, in addition to releases down the Middle Fork American River, the water is diverted into a tunnel to Ralston Powerhouse and into Ralston Afterbay, where it joins water from the pre-dam path. Oxbow Powerhouse and Oxbow control dam there releases water into the middle fork of the American River just below the spot of the historical confluence.
Placer County's 1961 bond approval allowed its water agency to seek out water supplies that were not already claimed by others. Loon Lake, south of Hell Hole, was already prescripted, but the rugged, untouched Hell Hole was not. In 1934, the State of California took steps to claim any unclaimed water rights along the American River's three forks. In 1962 the rights to the Rubicon River water were conveyed to Placer County.
The Hell Hole dam, a rock-fill-type dam, was completed across the Rubicon River in December 1964. As the reservoir began filling the dam sprung a leak during a flood event and failed completely the next day. The resulting flood washed down the Middle Fork of the American River and washed away the Greenville Bridge near Auburn. The Placer County Water Agency began a new dam which was completed two years later and has now stood for 42 years.