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In 1988, reports for seven of the reconnaissance investigations were published. Reports for the remaining two areas were published in 1989. Based on results of the first nine reconnaissance investigations, four detailed studies were initiated in 1988: Salton Sea area, Stillwater Wildlife Management area, middle Green River basin area, and the Kendrick Reclamation Project area. Eleven more reconnaissance investigations were initiated in fiscal year 1988: Oregon: South Dakota: Sacramento Refuge Complex Klamath Basin Refuge Complex Gunnison and Uncompahgre River basins and Sweitzer Lake Pine River Project Middle Arkansas River basin American Falls Reservoir Middle Rio Grande Project and Bosque del Apache National Wildlife Refuge Malheur National Wildlife Refuge Angostura Reclamation Unit Belle Fourche Reclamation Project Riverton Reclamation Project California: California-Oregon: Colorado: Colorado-Kansas: Idaho: New Mexico: Wyoming: All studies are done by interbureau teams composed of a scientist from the U.S. Geological Survey as team leader, with additional Geological Survey, U.S. Fish and Wildlife Service, and U.S. Bureau of Reclamation scientists representing several different disciplines. The reconnaissance investigations are directed toward determining whether irrigation drainage: (1) has caused or has the potential to cause significant harmful effects on human health, fish, and wildlife, or (2) may adversely affect the suitability of water for other beneficial uses. The Gunnison and Uncompahgre Rivers and Sweitzer Lake (fig. 1) were sel- ected for a reconnaissance investigation because selenium concentrations in the Gunnison River at a U.S. Geological Survey gaging station located down- stream from the U.S. Bureau of Reclamation's Uncompahgre Project exceeded background selenium concentrations for major rivers in the United States (Smith and others, 1987). The U.S. Bureau of Reclamation previously had identified the Uncompahgre Project area as a large contributor of salinity to the Upper Colorado River Basin, and the geologic formation that contributes a large part of the salinity also was a likely source of selenium. The Uncompahgre Project area has characteristics such as alkaline and potentially seleniferous soils, low precipitation, and high evaporation that can be indicators of possible problems associated with irrigation drainage (Sylvester and others, 1988). Also, the State of Colorado had reported large concen- trations of selenium in fish collected from Sweitzer Lake, a small reservoir near Delta. Purpose and Scope The purpose of this report is to describe the results of the reconnais- sance investigation of the Gunnison and Uncompahgre Rivers and of Sweitzer Lake. The report describes concentrations of selected trace elements and pesticides in water, bottom sediment, and biota and compares the analytical 4