Researchers say Lake Michigan's ecosystem is suffering from an influx of quagga mussels, which more than tripled in number in the lake from 2005 to 2007.
Tom Nalepa is with the National Oceanic and Atmospheric Administration. He says the invasion of quagga mussels has disrupted the lake, causing fish to be thinner and clogging intake pipes at power plants.
The United States has proposed regulations in an effort to prevent the spread of invasive species like the quagga and zebra mussels in the Great Lakes. If approved, the new rules would require oceangoing ships to flush their ballast tanks with salt water before entering the St. Lawrence Seaway.