Hell Hole Reservoir, artificial, crescent-shaped lake in the Sierra Nevada mountain range

Hell Hole Reservoir is a crescent-shaped artificial lake about 3.5 miles (5.6 km) long at full capacity, 10 miles (16 km) west of Lake Tahoe in the Sierra Nevada. Lower Hell Hole Dam, a concrete structure with vertical columns and a flat top, holds back the Rubicon River. Pale granite banks meet deep blue-green water, and a boom line curves across the surface. Small granitic islands grow and shrink with the water level.

Placer County voters approved financing for the water agency in 1961, and proposals for the dam date to 1958. The first Hell Hole Dam was partially complete when it collapsed on December 23, 1964; the replacement was finished in 1966, creating the reservoir on the Rubicon River. The agency sought drinking water for growing communities such as Auburn and Roseville, plus hydroelectric power.

The lake is reached via forest service roads and best visited during warmer months when access routes are passable. Visitors should prepare for uneven terrain and remote conditions.

The name comes from a deep canyon now drowned by the lake, not from any hole found during construction. The US Board on Geographic Names traces the first use of "Hell Hole" to a US Geological Survey map of 1894. In 1913 author George Wharton James visited the canyon and wrote: "Hell Hole? Then give me more of it."