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that were cool- or warm-water tolerant. In reach I of Lodore Canyon, seven native and eight introduced species and four hybrid sucker combinations were detected by electrofishing. Flannelmouth sucker, brown trout, common carp Cyprinus carpio, bluehead sucker, and redside shiner were the most common species collected, and represented 72 % of the total assemblage structure. Native species were 51 % of the total. In reach 2, seven native and seven introduced species and four hybrid sucker combinations were detected by electrofishing. Flannelmouth sucker, brown trout, bluehead sucker, mountain whitefish, and common carp were the most common species collected, and represented 87 % of all fish captured. Native species represented 62 % of the fish community. In reach 3, seven native and eight introduced species and four hybrid sucker combinations were detected by electrofishing. Flannelmouth sucker, brown trout, bluehead sucker, common carp, and mountain whitefish were the most common species collected, and represented 88 % of the total assemblage structure. Native species represented 56 of all fish captured. The appearance of red shiners was notable at this site. In downstream reach 4, eight native and 11 introduced species and five hybrid combinations were detected by electrofishing. Flannelmouth sucker, bluehead sucker, common carp, brown trout, and red shiners were the most common species collected, and represented 87 % of the total assemblage structure. Native species represented 63 % of all fishes captured. The only razorback sucker captured in this survey came from reach 4. The appearance of northern pike and the increased abundance of channel catfish Ictalurus punctatus, was also notable. Longitudinal distribution patterns of several other fishes were also of interest. Abundance of native bluehead and flannelmouth sucker, speckled dace, and mottled sculpin were similar across the four Lodore Canyon reaches. Mountain whitefish declined and roundtail chub and Colorado pikeminnow increased in abundance in a downstream direction. Salmonids comprised 28.7 % of the fish community in reaches 1-3 but declined to 13.3 % in reach 4. Brown trout, the dominant salmonid in reaches 1-3 of Lodore Canyon, was relatively rare in reach 4. Another cool-water taxa, white sucker, was more abundant upstream and declined downstream, a pattern opposite that for warm-water tolerant channel catfish. 19