Larger fish livers concern scientists

Monday, March 22, 1999 | 11 a.m.

Scientists have discovered enlarged livers in game fish taken from the Las Vegas Wash and the Muddy River, but it could take years to find out what causes the problem.

In the meantime, federal, state and local water experts said there is no need to ban fishing, swimming or boating in Lake Mead or the Las Vegas Bay.

No warnings will go out about the valley's drinking water either. Water from the Las Vegas Wash and the Muddy River enter the lake -- the valley's primary source of drinking water -- more than six miles upstream from the intake pipes.

UNLV fisheries biologist Jim Pollard said all the game fish collected in samples from the Las Vegas Wash and along a one-mile stretch where the Muddy River enters Lake Mead's waters had bigger livers. Fewer than 100 fish were collected from the two sites.

Fish from five other sites in the lake and upstream had normal livers. A total of 400 sports fish, including striped bass, large-mouth bass and catfish, were collected.

"I certainly would not discourage fishing or other recreational uses at Lake Mead based on this preliminary information," Pollard said. All that scientists can conclude right now is that the fish reacted to something in the water or the sediments that caused their livers to enlarge, he said.

If a fish is exposed to a toxin, such as a pesticide or insecticide, the liver grows larger to filter out the harmful material, Pollard explained to the Lake Mead Water Quality Forum meeting in Henderson on Thursday. If a bacteria or virus were attacking the fish, the liver would shrink, he said.

The U.S. Geological Survey discovered traces of insecticides and pesticides in the wash in 1996. Most of the chemicals the agency found in the water and bottom sediments are common in urban area runoff.

However, even if the fish were exposed to toxins, that would not necessarily make them inedible.

A study of sports fish tissues from Lake Mead and its local tributaries last year concluded that parts normally eaten by people contained no pesticides, herbicides or polychlorinated biphenyls (PCBs). The U.S. Environmental Protection Agency's laboratory in Richmond, Calif., performed the tissue analysis.

"The results of this evaluation found that there is no identified health concern to sport fishermen for the consumption of game fish species from Las Vegas Bay or Lake Mead," the study said.

The Clark County Health District, the Nevada Division of Environmental Protection and the National Park Service reviewed the study, which was done at the request of the Lake Mead Water Quality Forum. They concluded there was no need for a warning against fishing in the lake.

Even if the fish in Pollard's study had been exposed to toxins, warning signs would not be posted until scientists discover which chemicals are causing the liver problems, which could take years. There has never been a fishing advisory posted for the Lake Mead National Recreation Area.

The National Park Service, however, did post six swimming advisory signs in the Las Vegas Wash a year ago, advising people that treated sewage flowed along the channel that drains the entire valley. Those signs are still posted.