Some 180 million gallons of effluent are discharged into the channel each day from three wastewater treatment plants. The daily sewage discharge is expected to increase to 400 million gallons a day by 2050.

The USGS and U.S Fish and Wildlife Service tracked the channel from its origins, before the inflow from the sewage plants, to where it empties into Las Vegas Bay in the lake. Their findings: The amount of endocrine-disrupting compounds (including hormone treatments and other chemicals affecting reproduction) increased more than 646 times.

Not far from the mouth of the drainage channel — amid the fishing boats and sightseeing tours — water is sucked into a long pipe, destined for a drinking water treatment plant, then Las Vegas — thus beginning the cycle all over again.

Other communities in Nevada, as well as locales in California and Arizona, also draw on Lake Mead.

"Lake Mead is a fortuitous worst-case scenario" for study, said environmental toxicologist Greg Moller, holding a bottle of Lake Mead water he planned to take back to his lab at the University of Idaho. "You've got the wastewater, you've got the documented impact on wildlife, and you have drinking water uptake."

Although more than 8 million tourists, including 500,000 anglers, visit the reservoir annually, there are no warnings about the contaminants. No signs. No advisories.

That's not unusual. Scientists have been finding pharmaceuticals in hundreds of other public waterways across the nation and throughout the world — almost always without public fanfare, as documented in the AP investigation.

At the same time, scientists are looking for remedies. In Las Vegas, just off the Strip at the Desert Research Institute, microbial biologist Duane Moser optimistically held a tray of increasingly murky test tubes.

"We put a little bit of estrogen in here, and then we added a particular bacteria, and guess what? The bacteria are consuming the estrogen," he said. Someday, perhaps, scientists will be able to use these special bacteria to clean estrogen out of contaminated water.

"It's early, but it's promising," he said.