Eroding wetlands may affect water quality

      At a full capacity of 9.2 trillion gallons, Lake Mead, the nation's largest reservoir, is big enough to dilute most pollution.
      But recent studies of carp from the lake's Las Vegas Bay have turned up evidence of contamination from pesticides and industrial chemicals, specifically residues of DDT and PCBs, which have been banned for more than 20 years.
      Scientists are trying to determine if sport fish -- striped bass and catfish -- from Las Vegas Bay also are contaminated.
      In addition, local biologist Larry Paulson is worried about a second issue -- whether eggs from a potentially fatal parasite, cryptosporidium, are being carried by stream to Southern Nevada's drinking water intakes at Saddle Island, six miles from the Las Vegas Wash inlet.
      A 1996 study by the Bureau of Reclamation found that salts in this wastewater stream are mixing with cleaner water of the lower Colorado River. The area extends to within about 1 1/2 miles of Saddle Island, according to the study.
      Kay Brothers, director of the Southern Nevada Water Authority's Resources Department, said so far no harmful chemicals have surfaced at Saddle Island.
      "The quality is extremely good," Brothers said. "We've never seen any sign of any of these chemicals. We see nothing similar to that at the intake."
      About nine miles upstream of the bridge over Las Vegas Wash, water flows virtually in a straight shot, unchecked by vast wetlands that once filtered most of the parasites and some of the pollution.
      Paulson, a former University of Nevada, Las Vegas professor who has focused his research on Lake Mead's water quality, said erosion from the rapid flows -- 140 million gallons a day just from the treatment plants -- has led to the demise of reeds and cattails that once slowed the stream.
      Restoration efforts are under way near Henderson and upstream of Lake Las Vegas on Las Vegas Wash. The wash flows through conduits beneath Lake Las Vegas.
      Norma Cox, a member of Friends of the Desert Wetlands Park, said more than 2,000 acres of former wetlands upstream of Lake Las Vegas are targeted for restoration. Financed by a $13.3 million park bond that was approved by voters in 1990, the wetlands project includes trails for wildlife observers and structures to prevent erosion.
      Failure to completely restore the Las Vegas Wash wetlands could yield fatal consequences. In 1994, an outbreak of illness in Milwaukee and other U.S. cities was linked to cryptosporidium, said Paulson, a water quality consultant to the Nevada Seniors Coalition.
      The coalition, led by Ken Mahal, is challenging a proposed $1.7 billion project to expand Southern Nevada's water delivery system.
      Mahal and Paulson, in letters and appeals filed to government agencies that approved the project, thus paving the way for construction, have reminded government officials and the water authority that the 1994 cryptosporidium outbreak contributed to the deaths of 32 people and made 78 others sick, including 11 healthy children.
      Most of those affected, 63, had weakened immune systems from HIV, the virus that causes AIDS.
      Continued growth of the Las Vegas Valley's population, now at more than 1 million, plus water and sewage demands from 30 million visitors each year, will further complicate the already questionable water quality situation, Mahal and Paulson said.
      Also, a regulatory gap allows small businesses to discharge chemicals unchecked into the storm sewer, Paulson said.
      Paulson believes pollution from industry and toxic wastes could be controlled by using gravel pits along Las Vegas Wash to hold storm runoff. He said a diversion dam built along Pabco Road on the valley's east side would channel runoff to the gravel pits, where some pollutants could degrade before controlled dispersion into the wash.
      Excess storm water could also be used for construction and golf course irrigation.
      But Paulson says the valley's pollution woes won't be solved until controls are put on pesticides and toxic wastes discharged into the sewer and cleanup of contaminated ground water layers is finished.
      While scientists continue to search for pollution sources that might be contaminating carp, Nevada's Environmental Protection Division already has identified sites around the Basic Management Inc. industrial complex near Henderson.
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