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Table 2. Summary of habitat mapping categories utilized in the field mapping program for the Colorado River. No. Habitat Type No. Habitat Type 1 Backwater 17 Shore Riffle 2 Backwater Pool 18 Riffle/Chute 3 Pool 19 Chute 4 Debris Pool 20 Slackwater 5 Rootwad Pool 21 Isolated Pool 6 Eddy 22 Embayment 7 Edge Pool 24 Overhang Vegetation 8 Shoal 25 Cobble Bar 8a Sand 26 Rootwad Pile 8b Cobble 28 Sand Bar 9a Sand Shoal/Run 29 Tributary 9b Cobble Shoal/Run 30 Shoal/Riffle 10 Run 31 Island 11 Scour Run 32 Rapid 12 Shore Run 33 Irrigation Return 13 Undercut Run 34 Inundated Vegetation 14 Riffle/Run 35 Pocket Water 15 Riffle 36 Boulders 16 Riffle Eddy 37 Waterfall Biological Parameters-Biological parameters collected at each sample location included periphyton biomass, benthic detritus, and biomass of benthic macroinvertebrates. Periphyton was quantitatively collected from cobble-sized rocks. Chlorophyll-a content of these samples was used as a measure of periphyton biomass and was measured in the laboratory with a spectrophotometer. Benthic macroinvertebrates were collected at each sample location with a Hess sampler. Samples were preserved in alcohol and analyzed in the laboratory. Organic material from these samples was dried and weighed to provide estimates of detritus coarse particulate organic matter (CPOM). Drifting macroinvertebrates were collected using paired drift nets from each sample reach. Nets were set out at dusk and left out for one hour. Initial and final net velocities were measured and total volume filtered by the nets was calculated. Numbers and biomass of macroinvertebrates were measured in the laboratory. RESULTS As noted in Table 1, a number of physical, chemical and biological parameters were measured during the course of this investigation. The sample design (Table 3) provided data from various strata of the Colorado and Gunnison rivers during four time periods. Results 7