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~ co 0) ~ C c) The report showed that under historic 1941-66 conditions the average concentra- tion of total dissolved solids was about 0.74 tons per acre-foot (560 ppm) at Lee's Ferry, about 0.94 tons per acre-foot (690 ppm) below Hoover Dam, and about 1.02 tons per acre- foot (750 ppm) at Imperial Dam. Under expected conditions with all au- thorized projects and projects currently proposed for authorization in operation, the average concentrations were estimated to be 1.04 tons per acre-foot (770 ppm) at Lee's Fer- ry, 1.33 tons per acre-foot (980 ppm) below Hoover Dam, and 1.65 tons per acre-foot (1210 ppm) at Imperial Dam. Since the report considered an Upper Basin depletion of only about five million acre-feet per year, future concentrations would be higher than the reported values. Biological Studies of Selected Reaches and Tributaries of the Colorado River. This report by the Federal Water Pollution Control Administration presents the results of a biological field investigation made in 1966 of the Colorado River System. The re- port states that short reaches of Upper Basin tributaries are adversely affected by the dis- charge of toxic metals and chemicals from mining and ore processing activities, mine drainage, nutrients from discharges of municipal sewerage systems, and various in- dustrial activities that cause silt and sludge discharges. Irrigation water returns raised the temperature of receiving streams suffi- ciently to replace cold-water fish with warm- water fish on a number of tributaries. Ad- verse effects from all sources were dissipated from a distance of 2 to 20 miles downstream of the point of discharge. Nutrients entering Lake Mead from Las Vegas Wash are stated as being the most sig- nificant man-made pollution source in the Lower Basin affecting Colorado River water users. The nutrient content of the waters in the Lower Basin is increased by returns from the Colorado River Indian Reservation, Palo Verde Irrigation District, and from recrea- tional activities below Parker Dam. No ad- vc 80622-204 7-70 1M 44 verse effects were reported. Fishing down- stream of Imperial Dam is reported to be adversely affected by the silt discharged to the river from the All-American Canal desilt- ing basins. Pollution of the Upper Colorado River Basin. The Technical Advisory and Inves- tigations Branch of the Federal Water Pollu- tion Control Administration prepared a re- port, "Pollution of the Upper Colorado River Basin", based on field studies conducted dur- ing July and August 1966. The report is to be used as background information for plan- ning and projections by the Colorado River Basin Water O!:Jality Control Project. Four geographical areas within the states of Colorado, New Mexico, and Utah were in- vestigated. Dissolved oxygen was found to be near saturation at all stations except at untreated waste sources on the North Fork ofthe Gun- nison River and the Price River. Fecal coli- form densities greater than recommended for recreational use were found in the Upper Colorado River main stem downstream from Grand Junction and Fruita, Colorado; Price River downstream from Helper and Price, Utah; Gunnison-Uncomphagre River system downstream from Delta and Ouray, Colora- do; and San Juan River system downstream of Farmington, New Mexico, and Durango and Cortez, Colorado. Iron and manganese concentrations were found to be frequently greater than the U.S. Public Health Service Drinking Water Standards. Many concentrations of metals were above the toxic levels for aquatic life. In many reaches the total dissolved solids con- tent was raised from levels of under 500 ppm to levels of between 1000 ppm and 2000 ppm by return flows from irrigation.