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Cowlitz River Project

Washington's tallest: Mossyrock Dam

Tacoma Power's largest electricity generating facility is the Cowlitz River Project. It produces enough renewable hydroelectric energy to serve more than 135,000 Northwest homes.

The Cowlitz River Project produces hydroelectric power from the water stored behind Mayfield and Mossyrock dams. Built in 1963, Mayfield Dam forms 13-mile-long Mayfield Lake. Mossyrock Dam, built in 1968, stands 606 feet above bedrock and is the tallest dam in Washington state. The dam forms 23.5-mile-long Riffe Lake. Learn about changes to Riffe Lake levels in 2017.

See video of generators being rebuilt inside the Mossyrock powerhouse. 

In addition to producing hydroelectric power, the Cowlitz River Project provides outstanding recreational opportunities, nearly 14,000 acres of lands managed for wildlife habitat and a fisheries program that includes the Cowlitz Salmon Hatchery.

Enjoy camping, boating or fishing? Learn more about Tacoma Power's Mossyrock, Taidnapam and Mayfield Lake parks. The lakefront parks feature facilities for RV, tent and group camping as well as picnic areas and boat launches.

Tacoma Power’s rebuilt Cowlitz Salmon Hatchery and Cowlitz Trout Hatchery rear coho salmon, Chinook salmon, steelhead and cutthroat trout. Naturally-spawning adult fish are collected at the salmon hatchery barrier dam and trucked up stream above the dams. Downstream-migrating juvenile fish are collected and either hauled or diverted around the dams and continue their journey to the Pacific Ocean.

The 14,000-acre Cowlitz Wildlife Area, which surrounds Mayfield and Riffe Lake, is managed and enhanced for a variety of birds and animals including deer, elk, wood duck, osprey and bald eagle. Tacoma owns the wildlife area and the Washington Department of Fish and Wildlife manages it with funding from Tacoma Power.

A license for operating the Cowlitz River Project was issued in 2002. The emphasis of the license is the restoration and recovery of naturally-spawning salmon runs in the Cowlitz River.


Take a Tour

Free group tours of the Cowlitz River Project facilities are available by appointment to school, civic, business and recreational groups during regular working hours. To make arrangements for a tour, please click here to complete the form.