Zebra mussels (Dreissena polymorpha) are small, clam-like, aquatic animals. Native to Eastern Europe and Western Asia, the mussels were transported to the Great Lakes in the ballast water of ocean-going ships in the early 1990's. They've now spread all the way west to California as well as the Mississippi River system and its tributaries down to the Gulf of Mexico. The mussels' only predators are smallmouth and largemouth bass, but zebra mussel reproduction far exceeds bass appetites.

The species generates immense financial burdens. "They get into pipes, pumps and into propellers, and they certainly impact our native species of clams and other organisms," said Wendy Ralley, a water-quality specialist at Manitoba Water Stewardship.

To slow the advance of the mussels, the Manitoba government has established an invasive species hotline (1-877-867-2470) and is asking people who take their boats to areas with zebra mussels to check them thoroughly when they return home.

Although a definite concern, zebra mussels remove suspended sediments and toxic substances within the water, making it cleaner and clearer. This has allowed a number of native plants in the Great Lakes to make a comeback.