Problem: The U. S. Army Corps of Engineers built Cougar Dam on the South Fork McKenzie River in the 1960s. Biologists estimate the habitat above the dam once supported more than 4,000 returning adult spring Chinook. However, water released from the dam was cooler than pre-dam river temperatures in the spring and summer and warmer in the fall and winter. These temperatures resulted in reduced migration of adult fish and early emergence of juveniles.
Solution: The Corps modified the dam’s intake tower by adding adjustable weir gates and a wet well. The new features allow dam operators to selectively draw water from various depths of the reservoir and mix it to a temperature more closely matching pre-dam downriver conditions.