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Klamath River Bull Trout (Salvelinus confluentus)
Well known for their high-class habitat needs, brightly spotted bull trout are considered excellent indicators of fish habitat and water quality. Of all fish in the salmon family, bull trout require the coldest, clearest water and often cannot survive in low water quality conditions which may support other salmon and trout. The bull trout is known to have occupied at least 10 creeks in the Upper Klamath, though is now absent or severely declining in all its Klamath habitat.
Threat status: Bull trout are listed threatened by the US Fish & Wildlife Service throughout their range. All Klamath River populations have either been extirpated or are at risk of extirpation. Threats to Klamath River bull trout include competition and hybridization with nonnative brook trout, lack of connectivity between suitable habitat areas, and water quality and habitat degraded by agricultural water use, poor logging practices, and livestock grazing.
Distribution: The USFWS recognizes 7 bull trout populations within the Klamath basin, two of which are in Upper Klamath Lake, 3 of which are in the Sprague River, and one of which is on the Sycan River. Numerous other populations have already been extirpated, leaving these populations isolated from one another and at risk of extirpation. Klamath River bull trout as a whole are highly isolated from and genetically different than all other bull trout populations, and are considered important for the future of the species. They reside further south and in a 
warmer, drier climate than most inland populations, and they are the only population of bull trout to share habitat with suckers. In addition to the Klamath, Bull trout live primarily in coastal Washington, the mid-Columbia River basin, and the Upper Snake and Columbia River headwaters in Oregon, Washington, British Columbia, Montana and Nevada.
Ecology: Bull trout can be resident (living in streams) or migratory (migrating to lakes or even the ocean). They require water temperatures below 18 degrees celsius, complex habitat, good cover, clean spawning and rearing gravels, and unblocked migratory corridors. Resident bull trout may reach 10 inches long, while migratory bull trout can reach 35 inches long and weigh over 30 lbs.
Links & References:
National Academy of Sciences, 2004. Threatened and Endangered Fishes of the Klamath Basin. p. 184-5
US Fish & Wildlife Service Bull Trout Critical Habitat Unit homepage
US Fish & Wildlife Service Bull Trout Species Profile & Management Links