Reconnaissance Investigation of Water Quality, Bottom Sediment, and Biota Associated with Irrigation Drainage in the Gunnison and Uncompahgre River Basins and at Sweitzer Lake, West-Central Colorado, 1988-89 David L. Butler, U.S. Geological Survey Richard P. Krueger, U.S. Fish and Wildlife Service Barbara Campbell Osmundson, U.S. FIsh and Wildlife Service Andrew L. Thompson, U.S. Fish and Wildlife Service Steven K. McCall, U.S. Bureau of Reclamation Abstract During the last several years, there has been increasing concern about the quality of irrigation drainage and its potential harmful effects on human health, fish, and wildlife. This report describes the results of a reconnaissance investigation done during 1988-89 of the Uncompahgre Project, located in west-central Colorado. Water, bottom sediment, and biota samples were collected in the Gunnison and Uncompahgre River basins, and at Sweitzer Lake to identify potential water-quality problems that could be associated with the Uncompahgre Project. The Uncompahgre Project was selected for a reconnaissance investigation because unusually large selenium concentrations have been reported in the Gunnison River downstream form the project and in fish from Sweitzer Lake. Irrigation drainage from the Uncompahgre Project area contributes dissolved solids, sodium, sulfate, nitrite plus nitrate, selenium, boron, and uranium to the Gunnison and Uncompahgre Rivers. Selenium concentrations in some of the water samples collected from both rivers exceeded U.S. Environmental Protection Agency criteria for protection of aquatic life and the concentrations may be of concern for fish and waterfowl because of food-chain bioconcentration. The largest concentration of selenium from the Gunnison River was 10 micrograms per liter in a sample collected in July 1988 upstream from Escalante Creek. The largest selenium concentrations in the Uncompahgre River were in samples collected at Delta; concentrations were 33 micrograms per liter in November 1987 and 34 micrograms per liter in January 1988. The insecticide parathion was detected at concentrations exceeding the criteria for protection of aquatic life in both the Gunnison and Uncompahgre Rivers in samples collected in July 1988. Irrigation-drainage water discharging into Sweitzer Lake contributes dissolved solids, sodium, sulfate, nitrite plus nitrate, and selenium to the lake during the nonirrigation season. The maximum concentrations of dissolved solids, sodium, sulfate, selenium, boron, and uranium were in samples collected during January and March 1988 from the Garnet Canal diversion at Sweitzer Lake; selected maximum constituent concentrations were: 12,700 milligrams per liter of dissolved solids, 320 micrograms per liter of selenium, 800 micrograms per liter of boron, and 64 micrograms per liter of uranium. Water in the Garnet Canal during the nonirrigation season probably is irrigation-drainage water. Concentrations of selenium in four sets of water samples collected in Sweitzer Lake ranged from 10 to 25 micrograms per liter. The selenium concentrations in all water samples collected at Sweitzer Lake exceeded criteria for protection of aquatic life. Mercury was detected in water samples collected from the lake and from inflow into the lake in July 1988. Concentrations of selenium in bottom-sediment samples collected from the Gunnison and Uncompahgre Rivers were slightly greater than baseline concentrations for soils in the Western United States. There was substantially more selenium in bottom sediments from Sweitzer Lake; the selenium concentration was 41 micrograms per gram in a sample collected in January 1988. Selenium concentrations in fish and avian food items at Sweitzer Lake may be large enough for fish and wildlife to accumulate harmful amounts of selenium through biomagnification of selenium in the food chain. Selenium concentrations in all whole-body fish samples from Sweitzer Lake exceeded the 85th-percentile concentration of the National Contaminants Biomonitoring Program. The Maximum selenium concentration was 50 micrograms per gram dry weight in a carp sample from Sweitzer Lake. The maximum recommended daily intake of selenium for humans could be exceeded by eating catfish from Sweitzer Lake; three ounces of catfish fillet had about 502 micrograms of selenium. Concentrations of selenium in many whole-body samples form the Gunnison and Uncompahgre Rivers and three tributaries of the Uncompahgre Rover exceeded the 85th-percentile concentration of the National Contaminants Biomonitoring Program. The maximum selenium concentration in a fish sample collected from streams was 10.5 micrograms per dry weight in a carp collected from Dry Creek, a tributary of the Uncompahgre River. Selenium concentrations in bird livers, whole-body birds, and eggs collected at Sweitzer Lake and the Escalante State Wildlife Area were equal, and some of the selenium concentrations indicate significant exposure to selenium. The maximum selenium concentration in a bird sample was about 84 micrograms per gram dry weight in the liver of a western grebe collected at Sweitzer Lake. Most other trace-element concentrations were less than baseline concentrations or less than concentrations that might be harmful to fish and wildlife. There were concentrations of cadmium, copper, mercury, and zinc in some biota samples that exceeded background concentrations. Large concentrations of mercury were reported in two common merganser livers collected at the Escalante State Wildlife Area. DDE was detected in all biota samples that were analyzed for organic compounds. The maximum DDE concentration was 110 micrograms per gram wet weight in a whole-body killdeer that probably accumulated the DDE in its wintering areas outside of Colorado. Toxaphene was detected in 12 biota samples. Concentrations of the herbicide dacthal in three fish samples exceeded the maximum dacthal concentration reported by the National Pesticide Monitoring Program. The Colorado River downstream from the Gunnison River provides habitat for endangered fish and birds. The Uncompahgre Project area is a major source of selenium to the Gunnison River; the effects of the selenium on the endangered fish and birds are not known.