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PART III CAUSES AND IMPACTS OF SALINITY e Assuming a yield of 5.8 million acre-feet for the Upper Basin, this leaves approximately 1.8 million acre-feet to be developed. Consumptive use of water for irrigation within the basin and ex- ports from the basin were responsible for the largest depletions of the Colorado River, while reservoir evaporation and municipal and indus- trial uses account for a lesser depletion. River Acre-feet 2,114 3,473 271 50 3,525 2,847 12,280 e The major part of the transbasin depletions in the Upper Basin is made at higher elevations where the salinity concentrations are very low. This removal of high quality water results in the remaining flows downstream becoming more concentrated even though some salts are removed by the water delivered to another basin. Many transbasin diversions have been made over the years and an additional number will occur in the future. Water exported from the Upper Basin during the period 1941-72 aver- aged about 360,000 acre-feet per year. Completion of such large proj- ects as the Colorado-Big Thompson, Duchesne Tunnel, and Roberts Tunnel and more recent projects such as the San Juan-Chama, Fryingpan-Arkansas, and Homestake resulted in increased exports to about 726,000 acre-feet per year for 1976-80, with a peak in 1978 of 852,000 acre-feet. C. Effects of Water Quality on Water Users I. Recreation, Esthetics, and Fisheries The major instream uses in the Colorado River include hydro- electric power, propagation of fish and aquatic life, recreation (in- cluding swimming, water skiing, boating, rafting, etc.), and esthetics. A number of conflicts between water uses have become prominent issues in recent years. e There can be many tradeoffs in water quality, eutrophication, and esthetics both in the reservoir and downstream, depending on the depth of reservoir withdrawal and the flushing rate. The depth of with- drawal impacts the temperature and nutrient releases from a reservoir. These releases can now be controlled by the use of selective withdrawal structures; however, the optimum temperatures for cold water sport 14