Nelson Dam and Yakima River Watershed

Removal of eight-foot high Nelson Dam upstream of the city of Yakima is a key element of a watershed-wide plan supported by diverse interests to reduce flood risk, shrink costs, and improve fish passage.

Nelson Dam sits on the Naches River, an important salmon bearing river and the largest tributary of the Yakima River. Nelson Dam was built in the 1920’s and rebuilt in 1985 to allow better fish passage. However, river conditions frequently render the fish passage facilities inoperable. The dam diverts irrigation water for some 8,000 Yakima residents as well as orchards. Rock, gravel, and sediment have built up for several miles behind Nelson Dam, exacerbating upstream flooding of businesses, homes, and a road to the regional medical center. Downstream, Nelson Dam starves the floodplain of sediment.

Deconstructing Nelson Dam and replacing it with a structure better suited to public safety, river health, and recreation is part of a complex plan led by the City of Yakima and Yakima County. Removing two other diversions downstream and consolidating all withdrawals at Nelson is part of the overall plan.

The dam will be replaced with a roughened channel, a technically innovative but proven approach that allows the gravels and sediment built up behind the dam to move downstream, a critical part of a coordinated plan to greatly reduce flood risk for the community. The roughened channel also allows free passage of fish and whitewater boats while improving movement of gravels to fish spawning areas downstream.