Merwin

About Merwin

The primary purpose of Merwin is hydroelectric. The dam generates hydroelectric power by channeling water through turbines, converting the energy of flowing water into electricity. The dam is owned by Pacificorp (private). It impounds the Lewis River near Woodland, Wa.

The dam stands 313 feet tall and stretches 1,250 feet across, creates a reservoir covering 3,921 acres, has a maximum storage capacity of 422,000 acre-feet, and collects water from a drainage area of 726 square miles. Completed in 1931, the structure is well-established, with more than 75 years of service.

This dam carries a high hazard potential classification, which means that a failure or uncontrolled release of water would likely cause loss of human life. This classification reflects the consequences of failure, not the likelihood — it indicates that people live or work in the area downstream. Its condition is rated fair — the dam has minor deficiencies that are being addressed or do not pose an immediate safety threat. An emergency action plan is in place for this dam. The most recent inspection on record was 04/19/2022.

At 313 feet, this dam is taller than 99% of all dams in the United States.

Living Downstream

If you live or work downstream of this dam, consider taking these steps: learn your local evacuation routes, check whether your county emergency management office has a dam failure inundation map, and sign up for local emergency alerts. The Washington dam safety program can provide more specific information about emergency planning for this structure.

Search for dams near your address to see all dams in your area with hazard classifications and safety data.