Male fish that are growing eggs have been found in the Potomac River near Sharpsburg, W. Va. Nine male smallmouth bass taken from the Potomac were found to have developed eggs inside their sex organs, according to the U.S. Geological Survey. The mutation is likely caused by hormone-laced pollution from nearby sewage plants, feedlots, and factory farms.

Federal scientists say the gender mutations are related to a class of pollutants called endocrine disruptors, which short-circuit animals’ natural hormone systems. Some endocrine disruptors are hormones themselves-such as human estrogen from women taking birth-control pills or animal hormones washed downstream with manure-that can pass through sewage plants untouched. Others endocrine disruptors are hormone mimics-industrial chemicals or factory byproducts which confuse the body because they are chemically similar to natural hormones. In 2000, the first nationwide survey of endocrine disruptors found hormones in about 37 percent of streams tested.

The Potomac River is the main source of drinking water for the Washington metropolitan area and many upstream communities. It provides about 75 percent of the water supply to the 3.6 million residents of Washington and its Maryland and Virginia suburbs.

The Potomac fish are not the first to demonstrate intersex abnormalities. Similar findings were made last year about 170 miles upstream, in the South Branch of the Potomac in Hardy County, W. Va. County officials believe chicken waste from poultry farms, which utilize significant amounts of endocrine-disrupting chemicals, contributed much of the hormone-laced pollution. A recent survey of cancer in Hardy County, where some residents get drinking water from the South Branch, found rates of cancer of the liver, gallbladder, ovaries and uterus that were higher than the state average. All four cancers typically grow faster in the presence of estrogen or chemicals that mimic it.

The Environmental Protection Agency has not set standards for many of these pollutants. As a result, many drinking-water plants make no special efforts to remove environmental estrogens and other endocrine disrupters from municipal water supplies.