Lake and Reservoir Water Quality Status Nevada contains 131 publicly owned lakes and reservoirs. Of these, 21 are of a significant size and account for 94 percent of the total lake surface area in the state. According to Nevada's 1998 Water Quality Assessment 305(b) Report, sixteen (16) of the larger lakes have high enough quality to be categorized as fully supporting all current beneficial uses. Some water quality parameters for Lake Tahoe, Topaz Lake, Lahontan Reservoir, and Las Vegas Bay (Lake Mead) indicate water quality is impaired, but still supports most beneficial uses (Nevada Division of Environmental Protection, 1998a). Because Walker Lake, a desert lake at the terminus of the Walker River, contains high levels of dissolved salts and seasonally low oxygen levels, it has been classified in the state's 305(b) Report as not supporting beneficial uses. Primarily, the lake provides habitat for Lahontan cutthroat trout (LCT) fisheries and a variety of migratory and resident birds, as well as various water-dependent and wildlife related recreation activities. Upstream consumptive uses have reduced the amount of water reaching the lake. A long term lowering of the lake level is the major factor for episodes of degraded water quality that imperils aquatic life, including fishes. Concern over the Walker Lake ecosystem remains high.   Map and Photos of Walker Lake               Monitoring for Toxic Substances The NDEP and the state Department of Agriculture, as well as federal agencies periodically sample water bodies to test for the presence and levels of toxic contaminants. The 1998 U.S. Geological Survey (USGS) report, Water Quality in the Las Vegas Area and the Carson and Truckee River Basins, describes the occurrence of toxic contaminants (e.g., metals, pesticides, uranium) in surface water bodies in the most populated areas of the state. Between 1992 and 1996, water samples were collected above and below areas with intensive agricultural, mining, and urban land uses in the Truckee and Carson River basins and Las Vegas Valley (Colorado River system). Samples also were collected in areas of known natural sources of contaminants. In general, contaminants were present below areas of intensive land use, but usually at low levels. High arsenic concentrations were found in samples taken from Steamboat Creek, a Truckee River tributary, and agricultural drain water in the Carson Desert. Also, according to the USGS report, high uranium concentrations were found in samples taken from Las Vegas Wash and agricultural drains in the Carson Desert. Geothermal systems in the Reno-Sparks and the Carson Desert were found to contribute arsenic, boron and mercury by way of springs and shallow water-table aquifers connected to surface waters. Elevated mercury in the Truckee River sediments occurs below Steamboat Creek. Steamboat Creek transports mercury and other metals from both naturally occurring and man-made sources associated with geothermal and mineral resources. The sediments of the Carson River below Carson City contain high levels of mercury, most originating from the processing of Comstock-era ore along the river between Dayton and Carson City. Pesticides occurred in surface water samples taken downstream of all urban and agricultural areas, but at levels below the safe drinking water standards. Many samples contained detectable levels of more than one type of pesticide. Samples collected above urban and agricultural areas produced only one sample with one type of pesticide detected. Next Page -- Groundwater Quality Back to Table of Contents