You can't see them or smell them, but a toxic soup of chemicals used on farms, lawns and in personal care products is finding its way into the Potomac River and its tributaries, where it appears to be harming fish and may pose threats for people as well.

That's the warning from scientists and activists as they issued an annual report on the state of the "nation's river."  They renewed their call for government at all levels to take steps to curtail the use and release of "endocrine disruptors," powerful compounds that are linked to "intersex fish" in the Potomac.

Researchers first noticed fish in the Potomac with both male and female sex organs in 2002 while investigating a spate of fish kills there.  Abnormal fish have turned up in the river's South Branch and in the Shenandoah River in Virginia as well as in the Monocacy River in Maryland. 

Up to 80 percent of fish sampled have intersex conditions, and endocrine-disrupting chemicals, which mimic natural hormones in animals and people, have been detected at low levels throughout the watershed.  The compounds are widely used in livestock farming, in lawn care, and in personal care products like shampoos and skin lotions.

"I don't believe we're going to find one chemical or one source," said Vicki Blazer, a fish pathologist with the U.S. Geological Survey.  "What we're seeing is complex mixtures."  She added that in the area of the Potomac where she's been working, "we do feel agriculture is playing a major role, as well as suburban and urban runoff."

While studies have found relatively low levels of endocrine-disrupting compounds can interfere with reproduction and with disease resistance in fish and wildlife, the research has yet to pin down clear human health harm.  Advocates contend that's a result of too little scientific attention so far.

"Water treatment facilities are not yet required to screen for endocrine disrupting contaminants, so they end up in our tap water," said J. Peterson "Pete" Myers, chief scientist for nonprofit Environmental Health Sciences.  "We aren't sure exactly what level of exposure causes harmful effects to human health, but if the intersex fish phenomenon is any indication, there's a critical need for regulatory agencies and decision makers to start addressing this issue."

The Environmental Protection Agency recently pledged to reexamine dozens of widely used chemicals, including some endocrine disruptors.  But advocates want Congress to mandate more extensive analyses and controls on their use and release into the environment.

"These new pollutants, they don't set our rivers on fire, they don't wash up on our shore," said Hedrick Belin, president of the Potomac Conservancy.  "But this intersex fish thing is a clear signal that something is wrong.  It's time to take a much closer look at what's in our river water and in our drinking water."