| East Fork Russian River | |
|---|---|
 Course of the River through the Potter Valley in the north and Lake Mendocino. | |
   | |
| Location | |
| Country | United States |
| State | California |
| County | Mendocino County |
| Physical characteristics | |
| Source | |
| • coordinates | 39°20′42″N 123°07′02″W / 39.34500°N 123.11722°W |
| Mouth | Russian River (California) |
• coordinates | 39°11′23″N 123°11′59″W / 39.18972°N 123.19972°W |
• elevation | 623 ft (190 m) |
| Length | 15 mi (24 km) |
| Basin features | |
| River system | Russian River (California) |
| Tributaries | |
| • left | Adobe Creek, Burright Creek, Mewhinney Creek, Cold Creek |
| • right | Busch Creek, Williams Creek, Bevans Creek, White Creek |
| Waterbodies | Lake Mendocino |
East Fork Russian River is a 15 mi (24 km) long tributary of the Russian River in Mendocino County, California artificially connected to the Eel River via an interbasin diversion at the Potter Valley Project hydroelectric facility. It forms in the north of Potter Valley, flows south through this valley, then southwest through a mountain pass to Lake Mendocino, an artificial reservoir that empties into Russian River. At one time Clear Lake to the east drained through Cold Creek then along the lower part of East Fork Russian River through Coyote Valley to the Russian River proper. A few hundred years ago a massive landslide blocked this channel, and Clear Lake found a new outlet to the Sacramento River.
Cold Creek flows year round, while the upper part of East Fork Russian River used to dry up in the summer leaving isolated pools along its course. This changed when the Potter Valley Project was completed in 1908. The project involved construction of two reservoirs on Eel River to the north of the Russian River basin, and a tunnel to the head of Potter Valley that carried water from Eel River to a hydroelectric station that discharged into East Fork Russian River. The Eel River water was used to irrigate Potter Valley, and supplied water to Ukiah below the convergence with Russian River. In 1958 Coyote Dam was built on East Fork Russian River just above its mouth on Russian River, flooding Coyote Valley to form Lake Mendocino. The lake provides additional water storage as well as flood control.
The continuous flow from the Potter Valley Project changed the fish ecosystem in the Russian River by eliminating the warm, still pools that had been used for breeding by native fish. In the 1950s the state introduced poison to the river to eliminate "useless" fish species in favor of game species. The Coyote Dam prevented steelhead trout from returning upstream, so today the East Fork Russian River is dominated by rainbow trout. The section of the river that flows through the mountains between Potter Valley and Lake Mendocino includes stretches of white water that are challenging for kayakers and rafters.