Smivs writes "US researchers say they have developed an effective way to kill unwanted plants and animals that hitch a ride in the ballast waters of cargo vessels. Tests showed that a continuous microwave system was able to remove all marine life within the water tanks. The UN lists 'invasive species' dispersed by ballast water discharges as one of the four main threats to the world's marine ecosystems. For example European zebra mussels (Dreissena polymorpha) have infested more than 40% of the US's inland waterways. Between 1989 and 2000, up to $1B is estimated to have been spent on controlling the spread of the alien invader."