Bull trout, Salvelinus confluentus, are native to the McKenzie Basin and inhabit Cougar Reservoir and the South Fork McKenzie above the reservoir. The Columbia River distinct population segment, which includes McKenzie River bull trout, was listed as threatened under the ESA in June of 1998. Construction of the temperature control facilities required lowering the reservoir below minimum pool, reducing the area from 1260 acres to approximately 106 acres from April 2002 through December 2004. Because drafting the reservoir could adversely affect the bull trout population, the Corps funded this study to minimize impacts of construction on bull trout. To protect this population, we needed to understand the movement and habitat use of bull trout in the South Fork McKenzie watershed, and to develop an emergency plan should environmental conditions become detrimental to the overall health of the population.