Great Lakes Article:

New invasive species joins well-known zebra mussel in Lake Superior
Canadian Press
Published on Canada.com on January 12, 2007

DULUTH, Minn. (AP) - Another invasive species has been found for the first time in Lake Superior.

Tests recently confirmed the presence of the quagga mussel in Duluth-Superior Harbor. The quagga mussel resembles another well-known invader, the zebra mussel. Quagga mussels can live in deeper water than zebra mussels but aren't considered likely to spread far beyond the Duluth harbour.

Quagga mussels already are abundant in the lower Great Lakes. The mussels originally came from the Black and Caspian seas of Eastern Europe and are believed to have been carried into the Great Lakes in the ballast water of trans-oceanic ships.

The quaggas consume food that's essential for small fish. Fewer small fish in the lakes means a shortage of food for larger fish.