January 14, 2015 10:38 AM EST

Researchers warned that a cocktail of ingested medications has slipped past sewage treatment plants and gradually accumulated in Lake Michigan, threatening to alter the hormonal balance of local fish.

Researchers from the University of Wisconsin – Milwaukee’s School of Freshwater Sciences have detected traces of coffee, birth control pills and antibiotics in Lake Michigan’s waters, the Detroit Free-Press reports. The most prevalent drug was Metformin, a medication commonly used to treat Type 2 diabetes.

Fathead minnows exposed to Metformin at the same concentrations found in the lake exhibited unusual hormonal imbalances four weeks later. Male minnows, for instance, began to produce a hormone typically associated with female egg production, though researchers say they have not yet ascertained the long-term effects of the hormonal changes.

“It’s enough to raise an alarm bell that this might be something that causes changes in reproduction of fish,” study author Rebecca Klaper said.

Read more at Detroit Free-Press.

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