Pollution Suspected Cause of Anomaly in River's South Branch 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. 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...