Nevada Water Science Center

Endocrine Disruption in Lake Mead

previous studies provided information indicating that endocrine disruption is still occurring in fishes from Las Vegas Wash and Bay many years after it was first reported, particularly in male fish.The previous work did not collect sufficient data to assess how widespread the issues of intersex and tumors are in the fish populations of Lake Mead National Recreation Area. Were these observations an isolated incidence or are the findings indicative of population level effects?

Research Plan

This study collected a sufficient number of fish (30 male carp) to be able to statistically assess the prevalence of intersex and tumors at Las Vegas Wash, Las Vegas Bay, Overton Arm (control site), and Willow Beach. This study determined

  • the extent of gonadal anomalies in male common carp populations;
  • the spatial distribution of these anomalies within LAME;
  • associations between gonadal anomalies and a measure of reproductive fitness: sperm quality (mitochondrial function, apoptosis, DNA strand breaks, and motility);
  • the potential chemical cause(s) of abnormalities in Willow Beach fish.

In addition, the source of contaminants is unknown at Willow Beach, so this research is designed to assess possible sources (the fish hatchery, Hoover Dam, boats, contaminants in sediment) and determine which source is most likely.


A USGS Circular will be released in 2012. This Circular is a joint effort between USGS, National Park Service, U.S. Fish and Wildlife Service, Bureau of Reclamation, University of Nevada, Nevada Department of Wildlife, and Southern Nevada Water Authority.


Lake Mead is the largest reservoir by volume in the United States. Inflows of water into the lake stem from the Colorado, Virgin, and Muddy Rivers, as well as Las Vegas Wash, which has become perennial due increasing volumes of municipal wastewater discharge (Covay and Leiker, 1998) and urban runoff resulting from population growth. Concurrent with population increase within the Las Vegas Valley since the 1940s, the volume of treated effluent has risen, and presently comprises approximately 175 million gallons a day or 90 percent of total flows to the Las Vegas Wash into Las Vegas Bay. In addition to effects resulting from the nutrient-loading, several studies have identified various anthropogenic chemicals in water, sediments, and fish in both Las Vegas Wash and Las Vegas Bay relative to other sites within LAME.

NPS manages LAME, which hosts about 9 million visitors yearly including 500,000 anglers drawn to its world-class recreational fishery. The USFWS provides management for the federally endangered razorback sucker, a species unique to the Colorado River, and for more than 180 species of migratory birds that utilize the relatively scarce aquatic habitat that LAME provides in an otherwise arid desert landscape. Designated critical habitat for the razorback sucker includes all of Lake Mead to its full pool elevation. The largest populations of razorback suckers anywhere along the Colorado River are found within LAME, indicating that the health and status of this biological resource is of interest not only regionally (LAME) but also nationally. The multiple uses of Lake Mead for drinking water, recreation, wildlife habitat, and wastewater disposal clearly demonstrate the vital importance to LAME of maintaining water quality.

A number of studies carried out in the mid to late 1990s indicated that fish residing in the Las Vegas Wash and Bay exhibited endocrine disruption possibly due to exposure to anthropogenic chemicals in their aquatic environment. Most of these studies have used common carp as sentinel species for the health of razorback sucker populations. Since these studies were conducted, the southwest U.S. continues to experience a drought causing the level of Lake Mead, as well as other lakes in the region, to drop to historic lows. This change in hydrological conditions has likely concentrated and changed the patterns of contaminant and effluent distributions in the lake; consequently, the patterns of exposure of aquatic biota to contaminants may also have changed within the LAME. Moreover, an additional planned change is the diversion of wastewater from Las Vegas Wash into a deepwater site in Boulder Basin on the south side of the Lake. This planned diversion of wastewater into another section of the LAME will change the levels and extent of stressors within the ecosystem. Because of these concerns, studies have been recently implemented to reassess the status of endocrine disruption in Lake Mead.

Quick Facts


Location: Lake Mead, southern Nevada

Start Date: 2007

End Date: 2011

Cooperators: National Park Service, U.S. Fish and Wildlife Service, Texas Tech University, University of Nevada, Desert Research Institute

Contact Information


Michael Rosen

USGS Nevada Water Science Center

2730 N. Deer Run Rd.

Carson City, NV 89701

phone: (775) 887-7683





LAME: LAke MEad National Recreation Area

NpS: National park Service

USFWS: U.S. Fish and Wildlife Service


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page Last Modified: May 2, 2012