The fish in Las Vegas Bay look healthy on the outside, but it's what's inside that matters.

For more than a decade scientists have found that some fish in the bay and in the Las Vegas Wash, where treated wastewater is released back into Lake Mead, have mutated reproductive systems and different hormone levels than fish in other parts of the lake.

Now scientists are trying to determine whether those differences are the result of long-term exposure to releases of hundreds of millions of gallons each week of wastewater that contains trace amounts of hormones such as estrogen, as well as other chemicals and pharmaceuticals. Local water and wastewater managers are teaming up with federal agencies on a $1 million, two-year experiment that will test the effects of different kinds of wastewater on the reproductive systems of fathead minnows.

Starting this summer, scientists will raise generations of the minnows, stand-ins for the endangered razorback sucker and other native fish, in tanks at Clark County's wastewater treatment plant on Flamingo Road. They'll expose the little bait fish to the effluent that runs down the Las Vegas Wash into Lake Mead every day.

The goal is to see whether the wastewater - as opposed to ground water contaminated by local industry, chemicals in runoff, temperature differences or other factors - causes changes in the fish.

"When we look at the health of fish in the lake, you never know exactly what caused them (the changes) because they occurred over so many years," said Lynn Orphan, regional water quality manager for the Clean Water Coalition, one of the participating agencies. She added that it is important to "invest time and money into making sure our water is as clean as we can make it."

Scientists also hope to test whether new wastewater treatment techniques, including the use of ozone and special filters, lessen or eliminate the effects on fish.

In addition to the potential to improve the bay, wash and lake for fish, the study could also benefit humans. If the study helps scientists find new ways to improve water quality in Lake Mead, it would improve Las Vegas' drinking water supply and recreation and fishing opportunities, as well as conditions for other wildlife, said representatives of several of the agencies involved.

Full Story: http://www.lasvegassun.com/news/2008/apr/21/fish-story-true/