Four years ago, Heiko Schoenfuss’ study of pollutants in the Mississippi River attracted national media attention and raised alarm.

Schoenfuss, director of St. Cloud State University’s aquatics toxicology lab, found so-called endocrine disruptors – chemicals traced to everything from medications to cleaning products – were causing male fish to develop female reproductive traits.

For a Minnesota scientist, Schoenfuss’ next question was a logical one: What about lakes?

Unlike rivers, lakes typically aren’t a dumping ground for large industries and city wastewater treatment plants. Schoenfuss wondered if they are being affected by the same chemicals.

“Very few people have looked at lakes,” he said. “We thought that there was a very big void in our understanding.”

In the summer of 2008, Schoenfuss joined the state Pollution Control Agency and the U.S. Geological Survey to study endocrine disruptors in 11 Minnesota lakes. Their findings were published last month.

The researchers found what Schoenfuss calls “a very similar picture to what we find in rivers.” Endocrine-disrupting chemicals were found to be widespread in low concentrations in the lakes.

The research team chose lakes with a variety of characteristics – some large and some small, some shallow and some deep, some heavily used by humans and others nearly pristine. They were scattered across Minnesota from the Iowa border to Voyageurs National Park.