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e PART IV. COLORADO RIVER WATER QUALITY ASSESSMENT An important objective of this water quality investigation is to assess the suitability of Colorado River water for various beneficial uses. The Water Quality Office or Department of Health of each State was asked to submit an inventory of water pollution problems and/or priorities for users of the Colorado River water within its State. A. Wyoming Eutrophication of Flaming Gorge Reservoir.--Eutrophication of Flam- ing Gorge Reservoir is a major water quality problem. An overabundance of algae has resulted in use impairments in the Green River and Blacks Fork Arms of the reservoir. The impaired uses result from a shift from game to nongame fish species and decreased boating and fishing due to aquatic growth snagging propellers and fishing gear. Eutrophication has impaired the fishery, recreational, and esthetic value of the reser- voir. Flaming Gorge Reservoir is the most important recreational area in southwestern Wyoming. The 1978 Clean Water Report for Southwestern Wyoming estimated the economic benefits derived from recreation at over $8 million. e Studies indicate that the reservoir is phosphorus limited. Geologic or natural erosion is estimated to contribute 50 to 60 percent of the total phosphorus load. Municipal and private wastewater treatment plants contribute an estimated 11 percent of the load, while nonpoint sources such as overgrazed rangeland, channel modification, and manure runoff were identified as significant. Effective management strategies are limited by the lack of detailed knowledge regarding the limnology of the reservoir, conflicts between competing uses, and the fact that it may not be feasible to control the eutrophication rate so as to protect beneficial use. A task force has been established and a technical proposal developed involving the numerous State and Federal agencies involved with this problem. Salinity of Green River Basin.--The primary impact of salinity loads and concentration in the Green River system is on water users on the Lower Colorado River. The salinity levels in the Green River Basin within the State of Wyoming are generally within acceptable criteria for existing uses. Most of the increased load comes from the area encom- passing the Big Sandy River drainage. The salt loading is due to non- point sources associated with geologic erosion, overgrazing, irrigation return flows, and natural ground water discharges. e Although the water quality is generally adequate for industries, wildlife and livestock watering, and public water supplies, studies have identified some isolated problems and costs associated with these uses. Potential industrial and domestic benefits from salinity control are estimated to be $2 million per year. Impairment of wildlife and 16