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<br />. <br /> <br />. <br /> <br />. <br /> <br />a <br />c:D <br />IV <br />W <br /> <br />OTHER WATER QUALITY ASPECTS (Continued) <br /> <br />indicate serious pollution. Pesticides were tested for in samples of <br />fish flesh and water taken from the Wahweap and San Juan River arms of <br />Lake Powell. Pesticides found included DDD, DDE, and DDT. All levels <br />were well below the limits set by the Food and Drug Administration. <br /> <br />The Bureau of Sport Fisheries and Wildlife also ran pesticide tests <br />on fish flesh taken from Imperial Reservoir and Lake Havasu. Their re- <br />sults were very similar to those from Lake Powell. <br /> <br />6. Nutrients <br /> <br />Nutrients, primarily nitrogen and phosphorus, are believed to be <br />the most conducive to the growth of algae. The sources of these <br />nutrients are runoff from agricultural lands, municipal and industrial <br />waste waters, and natural runoff. Phosphorus is normally found in only <br />limited quantities in unpolluted water and the major contribution in the <br />Upper Basin appear to be from natural rather than agricultural sources. <br />Sufficient nitrogen is generally available naturally in basin waters to <br />stimulate algae growth. <br /> <br />Las Vegas Wash flows into Las Vegas Bay, an arm of Boulder Basin of <br />Lake Mead, and carries large loads of phosphorous and nitrogen. The <br />principal sources of water in the Wash are effluents from the Clark <br />County sewage treatment plant and the Las Vegas City sewage treatment <br />plant, which make up between 85-95 percent of the total flow. These <br />sources contribute about 80 percent of the nitrogen and 99 percent of <br />the phosphorous loading found in the Wash. <br /> <br />Several investigators have concluded that the nutrients carried in <br />the effluent from Las Vegas Wash contribute to the euthrophication and <br />degradation of Lake Mead. Nitrogen and phosphorous loads entering the <br />Lake through Las Vegas Wash total 600 and 150 tons (540 to 140 t) per <br />year, respectively. Chlorophyll A values (an indicator of algae mass) <br />have been measured in Las Vegas Bay which are 20 to 25 times greater <br />than comparable measurements in the main body of Boulder Basin. <br /> <br />The Environmental Protection Agency has identified these nutrients <br />as a cause of water quality degradation in Las Vegas Bay and, therefore, <br />causing a violation of the nondegradation provisions of the applicable <br />State-Federal water quality standards for Lake Mead and the Colorado <br />River. A notice of violation was issued to the municipalities and <br />industries discharging waste water into the Wash. <br /> <br />The nutrient load entering Lake Mead from the Wash has increased as <br />the municipal discharges to the Wash have increased. An advanced waste- <br />water treatment plant is now under construction which would strip the <br />phosphate from the effluent. <br /> <br />104 <br />