MONTREAL -- Petty Officer 2nd Class Travis Kelly, Marine Safety Detachment Massena, looks through a refractometer at a sample of ballast water from the motor vessel Eider in Montreal June 3, 2008.

The U.S. Coast Guard inspects all vessel's ballast water before they enter the Great Lakes to prevent invasive species inhabiting ecosystems. Photos by Petty Officer 3rd Class William B. Mitchell.