University of Michigan researchers are investigating a radical new design for cargo ships that would eliminate ballast tanks, the water-filled compartments that enable non-native creatures to sneak into the Great Lakes from overseas.

At least 185 non-native aquatic species have been identified in the Great Lakes, and ballast water is blamed for the introduction of most�including the notorious zebra and quagga mussels and two species of gobies.

This week, the U.S. Saint Lawrence Seaway Development Corp. will implement new rules designed to reduce Great Lakes invaders. Ships will be required to flush ballast tanks with salt water before entering the Seaway, a practice corporation officials describe as an interim measure, not a final solution.

Meanwhile, Congress is considering legislation that would force freighters to install costly onboard sterilization systems to kill foreign organisms in ballast water. The systems use filters, ultraviolet irradiation, chemical biocides and other technologies, and can cost more than $500,000.

The U-M ballast-free ship concept offers a promising alternative that could block hitchhiking organisms while eliminating the need for expensive sterilization equipment, said Michael Parsons, professor of naval architecture and marine engineering and co-leader of the project.