Some male fish in Washington's Potomac river, which provides drinking water to the city, have begun developing female sexual traits. Scientists attribute this to chemical pollution. Preliminary report of a recent study by the us Geographical Survey (usgs) shows that chemical pollutants in the river are responsible for endocrine disruption among fish.

While scientists are still studying the survey results to determine Potomac's water quality, the number of intersex fish in the river has left them startled. An earlier investigation by usgs had found some of the male fish in the Potomac producing immature eggs in their testes. The fish, dubbed "intersex fish', have also been found in other parts of the country, particularly in Potomac's tributaries.