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order of abundance, and represented 86% of the total assemblage. Native species represented 55% of all fishes captured, by number. The longitudinal pattern of increasing downstream species richness in electrofishing samples was due mostly to faster addition rate of warm-water tolerant species in a downstream direction as cold-water or cool-water species dropped out. Over all Lodore Canyon reaches, percent native fish in electrofishing samples declined from 63% in the 1994 to 1996 period to 39% in the 2002 to 2004 period. Native fish composition in Whirlpool Canyon reaches in 2002 to 2004 was slightly higher at about 56%; no comparative 1994 to 1996 data are available. Major differences in Lodore Canyon fish community composition in 2002 to 2004 electrofishing samples compared to 1994 to 1996 were increased distribution and abundance of channel catfish and smallmouth bass, and brown trout supplanted flannelmouth sucker as the most abundant species in reaches LD1 to LD3. Comparison offish community composition across the longitudinal gradient in Browns Park, Lodore and Whirlpool canyons, and Island-Rainbow Park between the 1994 to 1996 and 2002 to 2004 periods, seine samples.-Similar to electrofishing sample data, the fish community of the Green River, as measured by seine sampling suggested that upstream reaches supported relatively fewer species, and most were cold- or cool-water tolerant. In comparison, downstream reaches supported a community with higher species richness that was composed mostly of cool- or warm-water tolerant taxa (Tables 6 and 7). A total of 25 fish species were detected by seine sampling; species richness in seine samples in the Browns Park, LD 1 to LD4, WH 1 and WH2, and Island-Rainbow Park reaches was 14, 15, 15, 18, 20, 20, 14, and 18, respectively. The absence of six species in WH2 was due to absence of rare taxa: three native and three non-native. In the upstream Browns Park reach in 1994 to 1996, a total of five native and six introduced species and three hybrid suckers was captured. In descending order of abundance, fathead minnow, bluehead sucker, white sucker, flannelmouth sucker, and redside shiner made up 96% of the fish community. Native species represented 33% of the fish community, by number. Mountain whitefish and brown trout were also captured, as was a single juvenile sand shiner. In Browns Park in 2002 to 2004, a total of six native and eight introduced species and 23