"The discovery of eight shells no bigger than a fingernail in Maryland waters has signaled the arrival of the exotic zebra mussels that have caused an estimated $5 billion in damage to the Great Lakes.

If they spread, the invasive fresh-water mussels could threaten the less-salty waters of the Chesapeake Bay northward from Annapolis.

The zebra mussels found in Maryland apparently were transported on a recreational fishing boat that was plopped from a car trailer into the fresh waters of the Susquehanna River above Conowingo Dam. Whether that handful can get past the Harford County dam and into the Chesapeake may be a multibillion-dollar question."

Ashley Halsey III reports for the Washington Post Staff May 24, 2009. [2]