Mossyrock Dam
Mossyrock Dam is part of Tacoma Power’s Cowlitz River Project on the Cowlitz River in Lewis County. Completed in 1968, it is Washington state’s tallest dam at 606 feet above bedrock. The 1,648-foot-long concrete arch and gravity dam can generate a maximum of 382 megawatts of clean, renewable hydropower, enough to supply more than 87,000 Northwest homes annually.
The dam created Riffe Lake, a 23.5-mile-long reservoir with 52 miles of shoreline. Mossyrock Park and Taidnapam Park provide access to camping, boating, fishing and other outdoor recreation around the lake.
Questions? Reach out to Cowlitz@tacoma.gov.
At a Glance
- Completed: 1968
- Dam type: Concrete arch/gravity and embankment
- Height: 606 feet above bedrock
- Length: 1,648 feet
- Reservoir: Riffe Lake
- Reservoir length: 23.5 miles
- Shoreline: 52 miles
- Generating capacity: 382 megawatts
- Average annual generation: 1.1 billion kilowatt-hours
- Homes served: Approximately 87,300 Northwest homes annually
- Generators: Two
