MOOREFIELD, W.Va. -- The South Branch of the Potomac River is as clear as bottled water here, where it rolls over a bed of smooth stones about 230 miles upstream from Washington. But there is a mystery beneath this glassy surface.
Many of the river's male bass are producing eggs.
The Potomac's South Branch in Moorefield, W.Va. The bass problem was found after reports of many fish dying with lesions.
(Ricky Carioti -- The Washington Post)
Scientists believe this inversion of nature is being caused by pollution in the water. But they say the exact culprit is still unknown: It might be chicken estrogen left over in poultry manure, or perhaps human hormones dumped in the river with processed sewage. Chances are, it is not something that federal and state inspectors regularly test for in local waters.
The discovery has made the South Branch the latest example of an emerging national problem: Hormones, drugs and other man-made pollutants appear to be interfering with the chemical signals that make fish grow and reproduce.
While researchers look for answers in West Virginia, other scientists are testing Rock Creek, and another group is seeking financial support to test the rest of the Potomac to see whether they can find the same troubling effects downstream.
"Whatever's doing this to the fish may be the canary in the mineshaft," said Margaret Janes, a West Virginia activist with the Appalachian Center for the Economy and the Environment.
Scientists say it's still too early to tell what these findings will mean for the bass population in the South Branch; they aren't sure whether the affected males are still able to reproduce. And no one is aware of any effects on human health in the Potomac watershed.
But scientists believe that fish might be the first to absorb any dangerous chemicals that might later affect humans.
"They're likely to be hit first," said Mike Focazio, a researcher with the U.S. Geological Survey. "We look there, and it seems to be happening."
The situation in West Virginia was discovered by accident, when scientists from the state and the geological survey were called in to investigate reports that fish in the South Branch were developing lesions and dying en masse.
They dissected dozens of bass caught last summer, mainly smallmouth bass. They found no obvious cause for the lesions or deaths, but did discover that 42 percent of the male bass had developed eggs inside their sex organs.
The study surprised scientists. Though the South Branch has been cited for problems with bacteria from poultry manure, state officials said it did well on most aspects of water-quality testing.
"We always have, and still do, look at this as one of our highest-quality fisheries," said Patrick Campbell of the state Department of Environmental Protection. "It's counter-intuitive to think we would have this type of problem out there."
But the problem is there: A follow-up survey in the spring found even higher rates of "intersex" bass -- as the affected males are called. A study of 66 male smallmouths from the South Branch found that about 79 percent showed such symptoms, according to U.S. Geological Survey data.