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SUMMARY Electrofishing results in 2000 for species composition and size structure of fish over 15 em were similar and consistent with earlier years except for the Duffy stations on the Yampa River. Much attention was given to the large increase in smallmouth bass composition at Duffy in 2001. Reduction in total fish density from earlier years (1998 and 1999) on the Yampa River were explained by suggesting a reduced carrying capacity due to very low summer flows. Density estimates were higher in 200 I at the Com Lake and Clifton stations on the Colorado River than in 2000. It was suggested that fish abundance estimates in 2000 were biased low that year. Lily Park on the Yampa River was sampled dnly in 2000 and 2001. Fishery characteristics were somewhat different between years and grossly different from Sevens and Duffy stations. The observed differences in species composition, density, and sizes between Yampa sites appear to be a function of differences in meso-habitat availability (gradient, substrate particle size, riffle/run ratios) rather than differences in predatory pressure, temperature or water quality. The between years differences appears to be related to lower flows in 2000 and 2001. Flannelmouth sucker density at Lily Park was very similar to the Colorado River, and it is excepted that medi-run habitat composition will also be similar. Large differences were observed between the Yampa and Colorado River fisheries. The Colorado River has a different species composition, size structure and nlLlch higher total fish and native fish densities. Large predator fish were rare in the IS-Mile Reach and all size and age groups were present. In contrast, predator fish are common in the Yampa and obviously impacts that conununity. In general on the Yampa, there is a lack offish under 30 em, and higher mean lengths for virtually all species at Duffy and Sevens. Habitat analysis completed on the Duffy and Com Lake sites fOlmd very large differences in habitat composition between these two stations. Stream width and therefore total wetted area (habitat potential) at most flows of interest were higher at Duffy than at Com Lake. Habitat diversity peaked at 1,200 cfs at Com Lake and 180 cfs at Duffy. This is a function of greatly differing channel morphology between the sites. Most of the differences in species composition and density appear explainable by difference in habitat availability, and predation on the Yampa River impacted size structure. Riffle habitat is rare at Duffy but abundant at Corn Lake and suggests a direct relationship between riffle habitat availability and bluehead sucker density at these sites. Also the difference in 70 - 8