Pyramid Lake is an endorheic salt lake, approximately 188 square miles (487 km²) in area, in the Great Basin in the northwestern part of the U.S. state of Nevada. One of the largest lakes in the United States, it is located in southern Washoe County 40 mi (64 km) northeast of Reno, along the east side of the Virginia Mountains with a surface elevation of about 3,790 feet (1,155 m).
It is fed by the Truckee River (the outlet of Lake Tahoe), which enters the lake from its southern end. It has no outlet, with water leaving only by evaporation, or sub-surface seepage. The lake has about 10% of the area of the Great Salt Lake, but it has about 25% more volume. The salinity is approximately 1/6th of sea water. Although clear Lake Tahoe forms headwaters that eventually drain to Pyramid Lake, the Truckee River delivers more turbid waters to Pyramid Lake after traversing the steep sierra terrain and collecting moderately high silt-loaded surface runoff.
The lake is the largest remnant of ancient Lake Lahontan that covered much of northwestern Nevada at the end of the last ice age. Pyramid Lake was the deepest point in Lake Lahontan, reaching an estimated 890 feet due to its low elevation level relative to the surrounding basins. In the 19th century the vicinity of the lake was inhabited by the Paiute. The lake is now completely within the Pyramid Lake Indian Reservation. It was first mapped in 1844 by John C. Frémont, the American discoverer of the lake who also gave it its English title.
Major fish species include the cui-ui lakesucker, which is endemic to Pyramid Lake, the Tui chub and Lahontan cutthroat trout (the world record cutthroat trout was caught in Pyramid Lake). The former is endangered, and the latter is threatened. Both species were of critical importance to the Paiute people in pre-contact times. As they are both obligate freshwater spawners, they rely on sufficient inflow to allow them to run up the Truckee River to spawn, otherwise their eggs will not hatch. Diversion of the Truckee for irrigation since the early 20th century has reduced inflow such that it is rarely sufficient for spawning in modern times. Due to the construction of Derby Dam in 1903 made to divert water to croplands in Fallon, an adjacent town, the Lahontan cutthroat trout (the "salmon-trout" as described by Frémont) became extinct in Pyramid Lake and its tributaries due to the immediate lowered water level, increased water salinity, and lack of fish-ladders on the dam (for upstream spawning runs), and were replaced with Lahontan cutthroat trout from hatcheries. Fish populations are now sustained by several tribally-run fish hatcheries.
The name of the lake comes from the impressive tufa formations nearby. The largest such formation, Anaho Island, is home to a large colony of American White Pelicans and is highly restricted for ecological reasons. Access to the Needles, another spectacular tufa formation at the northern end of the lake has also been restricted due to recent vandalism.
Pyramid Lake is virtually a character in the classic novel of the Great Basin, City of Trembling Leaves, by Walter Van Tilburg Clark. The region was also rendered beautifully in the semi-abstract landscapes of Robert Caples, Clark's friend and the model for the character Lawrence Black in the novel.