Federal scientists say human and cattle viruses have been detected in some rivers within the Great Lakes watershed.
The U.S. Geological Survey and the U.S. Department of Agriculture tested 290 water samples from eight rivers between February 2011 and June 2013.
They found human viruses in 16 percent of the samples. They occurred most often and at highest concentrations in Michigan's River Rouge, followed by the Clinton River in Michigan and the Milwaukee River in Wisconsin.
Bovine viruses were found in 14 percent of collected samples. They were most common in the Manitowoc and Milwaukee Rivers in Wisconsin.
Scientists say human viruses can come from wastewater treatment infrastructure, malfunctioning sanitary sewers and septic systems.
Bovine virus sources can include direct cattle access to streams and flow from barnyards and pastures.
