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to improved water quality by diluting the high pollutant loads entering Lake Mead via Las Vegas Wash. Since July 1981, the municipal dischargers in the Las Vegas area have installed chemical addition, reducing the phosphate load to the wash by 90 percent. Attainment of this phosphate reduction has resulted in the associated reduction of biochemical oxygen demand and suspended solids loading from these municipal sources to the wash and the lake. Monitoring conducted during 1983 indicated a high concentration of chlorophyll-a in the inner Las Vegas Bay despite cutbacks in the phosphorus loading. The Virgin River, a tributary to Lake Mead, exhibited poor water quality in terms of bacteria, esthetics, and solids, and very minimal fish li fe . Phosphorus is of concern, chiefly with respect to present and future domestic use and, secondarily, with respect to recreation and fisheries. Studies have indicated that in-lake concentrations greater than 0.013 mg/L will produce algae concentrations which will have adverse effects on recreation, whereas other studies have implied that more phosphorus is necessary for fisheries. In view of this, Nevada adopted and implemented the requirements of no more than a mg/L of phosphorus for all point sources. The major point sources are the three large municipal facilities along the Las Vegas Wash. Salinity, hardness, sulfates, and chlorides are of concern with respect to domestic use of water from Lake Mead. The present levels appear to be accepted by the public, although an economic impact is felt as a result of additional treatment at the point of use and damage to plumbing. Nevada is doing its part in maintaining present levels by applying the salinity control policy of the Forum to control the industrial and municipal sources. Another major concern is the high concentration of ammonia in Las Vegas Bay. During 1985-86, un-ionized ammonia was observed to be above the chronic toxicity level. Also, a large blue-green algae bloom occurred in 1986 and had an adverse effect on the beneficial uses of the bay. F. California The salinity of the Colorado River is a matter of great concern to California. Southern California receives about 65 percent of its total water supply from the Colorado River, which provides a full water supply to about 800,000 irrigated acres and a full or supplemental supply to about 12 million people. Because California is located at the lower end of the Colorado River Basin, the water that it diverts contains all of the dissolved salts that have entered the river upstream. Colorado River water is used in California to grow many specialized high value crops such as avocados, dates, citrus fruits, grapes, and winter vegetables, as well as basic crops such as cotton, alfalfa, wheat, and sugar beets. Because of its high salinity, Colorado River water requires special management so that crop yields may be maintained and low-salt-tolerant plants will not be damaged or killed. Agricultural areas of California are already suffering significant economic detriments in their utilization of Colorado River water. Those detriments will increase if Colorado River salinity levels are allowed to increase with development of the Colorado River Basin. III-5