Trinity Dam is an earth dam on the Trinity River that forms Trinity Lake near Weaverville, California. Trinity Lake was previously called Clair Engle Lake. The 538-foot (164 m) earthfill dam was built by the U.S. Bureau of Reclamation. Construction was completed in 1962.
Trinity Lake has a capacity of 2,447,650 acre feet (3.01913×109 m3), making it one of the largest reservoirs in California. Trinity Lake and Dam are part of the Central Valley Project, which harnesses the waters from the Sacramento River and San Joaquin River watersheds to irrigate the Central Valley. The area around the reservoir forms one of the three units of the Whiskeytown-Shasta-Trinity National Recreation Area.
Trinity Dam forms an impassable barrier for migrating salmon in the Trinity River, but along with other division facilities has also had adverse impacts on salmon habitat in the lower reaches of the river. Within ten years of the dam's completion, more than three-quarters of Trinity River water was being diverted to the Central Valley each year, and the little flow left in the river was warm, shallow and less suitable for spawning salmon. In addition, the dam blocks the Trinity River's annual floods and sediment loads, leading to degradation in the gravel bars that are vital for salmon habitat.
In response to declining salmon populations, the USBR built the Trinity River Fish Hatchery. The hatchery is operated by the California Department of Fish and Game and has a capacity of 40 million eggs. In 1992, Congress passed the Central Valley Project Improvement Act, which established a minimum annual release of 340,000 acre feet (420,000 dam³) into the lower Trinity River.
With 145 miles (233 km) of shoreline, Trinity Lake is a popular summer destination for Northern California residents. Since 1965, the lake has been part of the Trinity Unit of the Whiskeytown-Shasta-Trinity National Recreation Area. The lake has been developed with boat ramps and marinas, most of which are concentrated in the Stuart Fork arm in the southwest and around the resort town of Trinity Center near the north end of the reservoir.