| Merwin Dam | |
| Coordinates: | 45.9567°N -122.555°W |
| Dam Crosses: | Lewis River |
| Res Name: | Lake Merwin |
| Location: | Clark / Cowlitz counties, Washington, USA |
| Operator: | Pacificorp |
| Dam Length: | 1250feet[1] |
| Dam Height: | 313feet |
| Construction Began: | 1929 |
| Opening: | 1931 |
| Res Capacity Total: | 422000acre.ft |
| Res Catchment: | 731sqmi |
| Res Surface: | 3921acres |
| Plant Commission: | 1931/1949/1958 |
| Plant Turbines: | 3 x 45 MW Francis-type, 1 x 1 MW[2] |
| Plant Capacity: | 136 MW |
| Plant Annual Gen: | 511,534 MWh |
Merwin Dam (also known as Ariel Dam) is a concrete arch gravity-type hydroelectric dam on the Lewis River, in the U.S. state of Washington. It is located on the border between Cowlitz County and Clark County. Its reservoir is called Lake Merwin.
On November 24, 1971, the dam was fully lit allegedly giving the skyjacker D. B. Cooper an identifiable landmark when he jumped from a Boeing 727 passenger liner. Cooper had ransomed 200,000 dollars from Federal Authorities after holding hostage the 727 and its passengers in Seattle.[3]