From the Harrisburg Patriot-News (November 30, 2008):
Zebra mussels (Dreissena polymorpha), normally native to Russia, have been found in the Susquehanna River above the Conowingo Dam in Maryland. Zebra mussels are an invasive species recorded from several locations in North America, including Texas, Massachusetts and the Great Lakes region. The species can clog drainage and intake pipes and kill off native species. Also, in the Great Lakes, they were associated with an outbreak of disease that killed off waterfowl.