<EM>ABSTRACT. </EM>Anadromous fish were excluded above Pelton Round Butte Hydroelectric Project (PRB Project), located midway (RM 100) on the Deschutes River in central Oregon, beginning in 1968. Reintroduction of these fish above the PRB Project is proposed to meet conservation concerns that arise from lack of natural production and separation of populations. One consideration, when moving fish groups that have been isolated one from the other for thirty years, is that of disease. The health of the fish populations above Round Butte Dam could be seriously jeopardized by the introduction of whirling disease. Straying hatchery steelhead trout <em>Oncorhynchus mykiss </em>were detected with <em>Myxobolus cerebralis </em>spores, in 1987, at Warm Springs National Fish Hatchery, below the PRB Project. <em>Myxobolus cerebralis </em>is established in tributaries of the upper Columbia River basin and of the Snake River basin, where some of these straying hatchery and wild steelhead trout may have originated. From 1997 to 2000, fish from the Deschutes River basin have been sampled for the presence of <em>M. cerebralis</em>. The parasite has been found in both straying hatchery and unmarked adult chinook salmon <em>O. tshawytscha </em>and steelhead trout. Presently there is no evidence of infection of resident fish or in returning adult fish originating from Round Butte Hatchery, although the potential for establishment of <em>M. cerebralis </em>in the Deschutes River watershed cannot be ruled out.
Assessing contributions of cold-water refuges to reproductive migration corridor conditions for adult salmon and steelhead trout in the Columbia River, USA
