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provinces and were grouped in more than one investi- gational category and in more than one land use. Algal Communities to- ~ en Q) Ten investigations between 1962 and 1987 incorporated algal-community information (table I, fig. 2). Sites in these studies were located in all predominant land-use categories and in both physiographic provinces (table I, fig. I). The algal data in these investigations were presented mostly as taxonomic identifications for the stream segments. The summaries of these investigations indicate that algal data are limited throughout the basin, but that algae are very useful indicators of water chemistry. Land use can affect types, numbers, and diversity of algae. Mining areas contain different taxa than that present in agricultural areas. For instance, in the UCOL study unit, investigations done in mining areas commonly contain certain species of green algae and diatoms because oftheir tolerance to acidic conditions and metals. Agricultural areas commonly contain blue-green algae as the predominant species because of its tolerance to higher concentrations of nitrogen from fertilizers (Stephen Porter, U.S. Geological Survey, oral commun., 1996). Macroinvertebrate Communities Fifty investigations between 1938 and 1995 included macroinvertebrate-community information (table I, fig. 3). Sites in these studies were located in a variety ofland uses and in both physiographic provinces (table I, fig. I). These investigations presented the data as taxonomic identifications or as numbers of organisms. Some of the investigations presented both types of data. The summaries of these investigations indicate there is an abundance of information on macroinvertebrate communities throughout the UCOL study unit. Land use can have direct effects on the composition of macro invertebrate communities. The use of indicator species for water-quality analysis is very common in studies of macroinvertebrate communities, especially when determining the water quality from mining effects. Macroinvertebrate- community composition can be different in mining areas than in agricultural areas. Mining areas commonly are depleted of aquatic organisms, but can contain metal-tolerant species. Agricultural areas commonly contain species, such as aquatic worms and leeches, that are tolerant of organic-carbon enrich- ment, sedimentation, and low dissolved-oxygen concentrations (Stephen Porter, U.S. Geological Survey, oral commun., 1996). Fish Communities Eighty-nine investigations summarized fish community or population information between 1938 and 1995 (table I, fig. 4). Sites in these studies were located in a variety ofland uses and in both physio- graphic provinces (table I, fig. I). The information on fish was presented as taxonomic identifications or as numbers of fish. Some of the investigations presented both types of data. The summaries of these investiga- tions indicate that information on fish communities is extensive throughout the UCOL study unit. Fish communities are an important issue in the UCOL study unit; the study unit contains four fishes presently listed as endangered by the U.S. Fish and Wildlife Service (USFWS) (Behnke and Benson, 1980): the Colorado squawfish (Ptychocheilus lucius), the humpback chub (Gila cypha), the bonytail chub (Gila elegans), and the razorback sucker (Xyrauchen texanus). In addition, recreational fishing in the study unit is important to many anglers. Historically, native fauna consisted of the following minnows and suckers in addition to those fishes listed above: roundtail chub (Gila robusta), llannelmouth sucker (Catostomus latipinnis), speckled dace (Rhinichthys osculus), kendall warm springs dace (Rhinichthys osculus thermalis), and bluehead sucker (Catostomus discobolus) (Tyus and others, 1982). The current fauna of the Colorado River is dominated by exotic species. All of the big river fish that were native to the area, except for the speckled dace, llannelmouth sucker, bluehead sucker, and roundtail chub, face extinction. The cause of the disappearance of some of the native species is due to loss of habitat and competition from other species (Ward and others, 1986). Native fish in the upper reaches of the basin included mountain sucker (Catostomus platyrhyn- chus), mountain whitefish (Prosopium williamsoni), mottled sculpin (Cottus bairdi), and Colorado cutthroat trout (Salmo clarki pleuriticus). 20 Summary ot Biological and Contaminant Investigations Related to Stream Water Quality and Environmental Setting In the Upper Colorado River Basin, 19~5