Topaz Lake, Reservoir at California-Nevada border, United States.

Topaz Lake is a reservoir on the California-Nevada border, about 75 miles south of Reno. It was formed by diverting the West Walker River into a basin that held a smaller natural lake. The reservoir covers 2,410 acres, is 3.5 miles long and 1.5 miles wide, with a maximum depth of 92 feet. The Topaz Lake census-designated place lies along its northwest shore.

The original dam project began in the early 1920s to capture water for agricultural irrigation in the region. A major reinforcement of the structure took place in the mid-1930s, significantly increasing the water storage capacity.

The lake lies on the route Jedediah Smith took in late spring 1827, when he left California after his first journey, the first crossing of the Sierra Nevada by a non-native. He came southeast through Monitor Pass and east past the lake into Nevada. The Topaz Lodge and a residential area stand on the northwest shore.

The lake is open year-round for fishing, with regular stocking programs managed by wildlife departments from both states. Visitors should check local regulations and access conditions, as these may vary by season or during maintenance periods.

The reservoir was created by diverting the West Walker River into a basin that previously held a smaller natural lake. This merger of engineered waterway and existing lake formed an unusual water body that blends two different water sources.