The zebra mussel is a barnacle-like shellfish that poses a multi-billion-dollar threat to industrial, agricultural and municipal water supplies across North America. Since it was spotted in the Great Lakes in 1988, it has become a nuisance for shipping, boating, fishing and clamming in freshwater as well. Experts believe this invader has the potential to cause more economic damage than the Mediterranean fruit fly. (Zebra Mussel Frequently Asked Questions)

How to identify a zebra mussel:

• Zebra mussels look like small clams, with a yellow or brownish D-shaped shell, often with dark and light-colored stripes.
• They can be up to two inches long, but most are under an inch.
• They usually grow in clusters, and are generally found in shallow (6-30 feet) water.
• Zebra mussels are the only freshwater mollusk that can attach itself firmly to solid objects - submerged rocks, dock pilings, boat hulls, water intake pipes, etc.
• A Zebra Mussel Field Guide

How did they get here? Scientists believe zebra mussels arrived in the Great Lakes by way of ballast waters in transoceanic ships, which come to the Midwest via the St. Lawrence Seaway.

Where are they now? Where are they going? Zebra mussels have been found in 52 inland waters in Wisconsin. Check out the distribution in the United States (1988 to current USGS maps).

What can I do?