Lewiston Dam, Embankment dam in Trinity County, United States

Lewiston Dam is a 91 ft (28 m) earthfill dam on the Trinity River near Weaverville, California, built by the U.S. Bureau of Reclamation and completed in 1963. It creates Lewiston Lake and includes a small hydroelectric power station. Most of the river's water is diverted through a 17.2 km tunnel toward the Sacramento Valley.

The U.S. Bureau of Reclamation completed Lewiston Dam in 1963, seven miles downstream of Trinity Dam, as part of the federal Central Valley Project. The project carried Trinity River water through a 17.2 km tunnel to the Sacramento Valley for irrigation of the San Joaquin Valley.

The Trinity River system modified by this structure holds deep meaning for Native American communities who depended on these waters for centuries. Local residents today relate to the landscape through the changes the dam has brought to water flow and ecosystem patterns.

The dam can be accessed from nearby roadways, with the clearest views from the eastern bank of the river. Visitors should expect uneven terrain and check local conditions before planning a visit.

The facility features specialized fish passage systems designed to allow salmon and steelhead to migrate through the waterway. These engineering solutions represent an effort to balance power generation with protection of native fish populations.