No more gobies

University of Michigan researchers are investigating a new design for cargo ships that would eliminate ballast tanks, the water-filled compartments that enable non-native creatures to enter 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 zebra and quagga mussels and two species of gobies.

This week, the US Saint Lawrence Seaway Development Corporation 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, the US Congress is considering legislation that would force freighters to install costly onboard sterilisation 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.