French Lake Reservoir, reservoir in Nevada County, California, United States

French Lake Reservoir is a reservoir in Nevada County, California, held back by the earthen, rock-fill French Lake Dam across Canyon Creek. The dam rises 100 feet (30 m) and measures 300 feet (91 m) along its crest. The reservoir covers 337 acres (136 ha) and holds up to 13,800 acre-feet (17,000,000 m3), surrounded by Tahoe National Forest.

The earthen, rock-fill French Lake Dam was first built in 1859 and is a candidate for the first engineered rock-fill dam. It was reconstructed in 1948, not raised, and impounds Canyon Creek for flood control, irrigation, municipal drinking water and hydropower. It is one of ten facilities run by the Nevada Irrigation District.

The reservoir sits at about 2,035 metres in the Tahoe National Forest, and the surrounding terrain is pine forest. Snow and mountain weather can affect access in winter, so check conditions before setting out. The dam crest is 300 feet long and the water surface covers 337 acres, giving a sense of the scale to plan around.

The dam was an early experiment in using stone and earth as building materials for water barriers, influencing modern dam construction techniques. This 19th-century engineering approach demonstrated that natural materials could effectively store water on a large scale.