Merwin Reservoir Report
Nearby: Elmer Dam Fargher Lake Dam
Last Updated: December 14, 2025
Merwin, located in Woodland, Washington, is a private hydroelectric dam on the Lewis River that was completed in 1931.
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Summary
With a dam height of 313 feet and a storage capacity of 422,000 acre-feet, Merwin serves multiple purposes including fish and wildlife pond management, hydroelectric power generation, and recreation. The dam is classified as an arch type, with a spillway width of 166 feet and controlled spillway type.
Managed by the Federal Energy Regulatory Commission, Merwin poses a high hazard potential and is considered to have a very high risk level. Despite its age, the dam's condition assessment is not available, and its last inspection was conducted in September 2020. The emergency action plan for the dam was last revised in February 2021, ensuring that necessary measures are in place to address any potential risks or emergencies that may arise.
For water resource and climate enthusiasts, Merwin presents an intriguing case study of a historic dam with significant storage capacity and operational capabilities. Its location on the Lewis River in Cowlitz County, Washington, provides a vital source of hydroelectric power while also supporting local wildlife and recreational activities. As efforts continue to monitor and manage the dam's risk levels, the importance of sustainable water resource management and infrastructure maintenance is underscored by Merwin's role in the region.
Year Completed |
1931 |
Dam Length |
1250 |
Dam Height |
313 |
River Or Stream |
Lewis River |
Primary Dam Type |
Arch |
Surface Area |
3921 |
Hydraulic Height |
230 |
Drainage Area |
726 |
Nid Storage |
422000 |
Structural Height |
313 |
Outlet Gates |
Tainter (radial) - 5 |
Hazard Potential |
High |
Foundations |
Rock |
Nid Height |
313 |
Seasonal Comparison
Weather Forecast
Nearby Streamflow Levels
Lewis River At Ariel
|
23800cfs |
East Fork Lewis River Near Heisson
|
2980cfs |
Speelyai Creek Near Cougar
|
14cfs |
Canyon Creek Near Amboy
|
1340cfs |
Burnt Bridge Creek Near Mouth At Vancouver
|
37cfs |
Columbia Slough At Portland
|
5cfs |
Dam Data Reference
Condition Assessment
SatisfactoryNo existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
Fair
No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action. Note: Rare or extreme event is defined by the regulatory agency based on their minimum
Poor A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency. Investigations and studies are necessary.
Unsatisfactory
A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
Not Rated
The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Not Available
Dams for which the condition assessment is restricted to approved government users.
Hazard Potential Classification
HighDams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
Significant
Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environment damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
Low
Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
Undetermined
Dams for which a downstream hazard potential has not been designated or is not provided.
Not Available
Dams for which the downstream hazard potential is restricted to approved government users.
Merwin
Merwin Hatchery Court, Ariel