McLean, VA (AHN)-Raising concerns about pollutants in a waterway that provides drinking water for millions of people, some species of male fish in the Potomac River and its tributaries are developing female sexual traits at a frequency higher than scientists have witnessed before.

While the so-called "intersex fish" have been found in other parts of the country, the frequency is much higher in the Potomac than elsewhere, according to fish pathologist Vicki Blazer.

Blazer says researchers are still waiting on data that would help them determine the water quality at the time the fish were caught, but preliminary data taken from the Potomac suggests a variety of chemical pollutants.

Certain chemicals and pesticides are believed to stimulate estrogen production. Also, estrogen from birth control pills and human waste can make its way from sewage treatment plants to the waterways.

The water authority, which draws from the Potomac and Occoquan rivers to provide service to roughly 1.5 million people, is working with U.S. Geological Surveys (USGS) and other agencies to research and develop ways to improve water treatment to eliminate potentially harmful compounds.

Meanwhile, Jeanne Bailey, a spokeswoman for Fairfax Water, says the findings are a concern, but cautions against drawing dire conclusions about the impact on human health, saying "Fish are a great indicator of the health of our waters, but they are not a great indicator of what may translate to humans."