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Land use can have variable effects on the structure offish communities. Intensely mined areas can be depleted offish. Fish communities in agricul- tural areas most likely contain species, such as suckers, carp, and catfish, that tolerate gravel, sand, and silt substrates in slower and warmer waters. The more pristine headwater reaches and mountain streams can contain brook, brown, rainbow, and cutthroat trout. Habitat Characterization Fifty investigations between 1959 and 1995 included habitat-characterization information (table 1, fig. 5). Sites in these studies mostly were located in areas of hydrologic modifications and in both physio- graphic provinces, but primarily are limited to the Colorado Plateau (table 1, fig. 1). Habitat information from these studies mainly consisted of stream substrates, channel width, channel depth, channel morphology, and flow. Hydrologic modifications can alter flows and degrade the necessary habitat for endangered species and fish communities. Habitat in the headwater and mountain streams is characterized by coarse substrate, such as boulders and cobbles; swift and cold water; and riparian vegetation. The lower reaches of the study unit contain fine substrates, such as gravel, sand, and silt; warm water; and less riparian vegetation. Contaminants in Organism Tissue Sixteen investigations between 1970 and 1994 summarized information about contaminants in tissue (table 1, fig. 6). Sites in these studies were located in a variety of land uses and in both physiographic provinces (table 1, fig. 1). Three of the studies contained information on organic and on trace- element contaminants (table 1, citation numbers 18, 19, 64). One study contained information solely on organic contaminants (table 1, citation number 66). The remaining twelve studies contained information solely on trace-element contaminants. A variety of organisms, which includes aquatic plants, macroinver- tebrates, fish, and other vertebrates, was used in the studies. The summaries of these investigations indicate that the watersheds for the Fraser, Blue, Eagle, and Roaring Fork Rivers have very limited data on contaminants in tissue. Specific contaminant constituents can be directly related to land use and geology in the UCOL study unit. Organic-contaminant investigations were most common in agricultural areas, and trace-element contaminant investigations were most common in mining areas. Investigations solely for collection of trace-element contaminant data mostly were done in the Southern Rocky Mountains physiographic province, whereas investigations for collection of both organic-contaminant and trace-element contaminant data were done in the Colorado Plateau physiographic province, especially in the Grand and Uncompahgre Valleys. Contaminants in Bed Sediment Seven investigations between 1963 and 1994 included information on contaminants in bed sediment (table 1, fig. 7). Sites in these studies mostly were located in agricultural and mining areas and in both physiographic provinces (table 1, fig. 1). Five of the studies contained information on organic and on trace- elementcontaminants (table 1, citation numbers 3, 18, 19, 24, 110). Two studies contained information solely on trace-element contaminants (table 1, citation numbers 28, 91). The summaries of these investiga- tions indicate that bed-sediment information is limited throughout the UCOL study unit. Bed-sediment contamination can be directly related to land use and geology. Trace-element and organic contaminants often are more concentrated in bed sediments than in water. Trace-element analyses are the most common analyses done in the bed- sediment investigations. The National Uranium Resource Evaluation (NUKE) program has an extensive data base on selected trace elements in the UCOL study unit. Investigations done on stream reaches in the headwater areas of streams were solely trace-element investigations. The lower reaches in the valleys were investigated for trace elements and organic compounds. 24 Summary of Biological and Contaminant Investigations Related to Stream Water Quality and Environmental Setting in the Upper Colorado River Basin, 1938-95