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Summary of Biological and Contaminant Investigations Related to Stream Water Quality and Environmental Setting in the Upper Colorado River Basin, 1938-95 By Jeffrey R. Deacon and Verlin C. Stephens ABSTRACT As part of the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) program, an inventory of the biological and contaminant investigations for the Upper Colorado River Basin study unit was conducted. To enhance the sampling design for the biological component of the program, previous studies about the ecology of aquatic organisms and contami- nants were compiled from computerized literature searches of biological data bases and by contacting other Federal, State, and local agencies. Biological and contaminant investiga- tions that have been conducted throughout the basin since 1938 were categorized according to four general categories of biological investiga- tions and two categories of contaminant investi- gations: algal communities, macroinvertebrate communities, fish communities, habitat character- ization, contaminants in organism tissue, and contaminants in bed sediment. The studies were identified by their locations in two physiographic provinces, the Southern Rocky Mountains and the Colorado Plateau, and by the predominant land use in the area of the investigation. Studies on algal communities and contaminants in organism tissue and in bed sediment are limited throughout the basin. Studies on macroinvertebrate and fish communities and habitat characterization are the most abundant in the study unit. Natural and human factors can affect biological communities and their composition. Natural factors that affect background water-quality conditions are physiog- raphy, climate, geology, and soils. Algae, macroinvertebrates, and fish that are present in the Southern Rocky Mountains and the Colorado Plateau physiographic provinces vary with altitude and physical environment. Green algae and diatoms are predominant in the higher altitude streams, and blue-green, golden-brown, and green algae are predominant in the lower altitude streams. Caddisflies, mayflies, and stoneflies are the dominant macroinvertebrates in the higher altitudes, whereas aquatic worms, leeches, and dragonflies are more common at lower altitudes. Cold-water species, such as trout, are present at the higher altitudes, and warmer water species, such as catfish, carp, and suckers, are predominant at the lower altitudes. Human factors that affect water-quality conditions are mining, urbanization, agriculture, and hydrologic modifications. Mining areas can be depleted of organisms or contain a low diversity of species. Acid-tolerant algae, such as certain species of green algae and diatoms, and metal-tolerant caddisflies can be present in mining areas. Urbanized areas are located in the Southern Rocky Mountains and in the Colorado Plateau and contain species characteristic of the physio- graphic provinces. Agricultural areas contain species, such as blue-green algae, aquatic worms, suckers, and carp, that can tolerate organic enrich- ment, sedimentation, and lower concentrations of dissolved oxygen. INTRODUCTION The National Water-Quality Assessment (NAWQA) program is a long-term program by the U.S. Geological Survey (iJSGS) designed to describe Abstract