Mossyrock Dam
| Mossyrock Dam | |
|---|---|
| Location | Lewis County, Washington, U.S. |
| Coordinates | 46°32′4″N 122°25′43″W / 46.53444°N 122.42861°W |
| Construction began | 1965 |
| Opening date | 1968 |
| Construction cost | $117,769,400 |
| Operator(s) | City of Tacoma |
| Dam and spillways | |
| Type of dam | Concrete, arch-gravity |
| Impounds | Cowlitz River |
| Height | 606 feet (185 m) |
| Length | 1,648 feet (502 m) |
| Spillway type | Service, gate-controlled |
| Reservoir | |
| Creates | Riffe Lake |
| Total capacity | 1,685,000 acre-feet (2.08 km3) |
| Catchment area | 1,042 square miles (2,700 km2) |
| Surface area | 11,830 acres (4,790 ha) |
Mossyrock Dam is a concrete arch-gravity dam on the Cowlitz River near Mossyrock in Lewis County, Washington, United States. The reservoir created by the dam is called Riffe Lake. The primary purpose of the dam is hydroelectric production while flood control is a secondary function. The dam is the tallest in Washington state and its hydroelectric power station supplies 40% of Tacoma Power's electricity.