BALTIMORE, MD (January 7, 2013) – The Maryland Department of Natural Resources (MDNR) reports that zebra mussels (Dreissena polymorpha) have now spread to the upper Chesapeake Bay. This freshwater mollusk, native to eastern Europe, has rapidly proliferated throughout North America after first being spotted in the Great Lakes in the late 1980s.

Mature zebra mussels grow to two inches in length and usually have a striped pattern, thus their name.   Females can produce up to 1,000,000 eggs per year. These eggs are carried by currents and can easily infest other bodies of water. The mature mussels attach themselves to boats, and those boats can spread the mussels to other bodies of fresh water.   

Why are they a concern?

Just as with any plant or animal invasive species, zebra mussels can have a devastating impact on native wildlife. They colonize in large clusters, including on slow-moving aquatic creatures like crayfish, clams and turtles. In some cases the host animal does not survive. 

Zebra mussels are filter feeders, rapidly removing algae from water. While this improves water clarity, it can be harmful to fish and other aquatic life that depend on algae as a principal food source. 

These mollusks also colonize water intake pipes. If they enter Baltimore’s Liberty, Loch Raven and Prettyboy Reservoirs, they can restrict the water flow to our municipal treatment plants. Physical and chemical removal of them can be done; however it is costly and time-consuming. Zebra mussels can also create navigational hazards and damage piers, docks and bridges.   

 What can you do to prevent their spread?

The Department of Public Works has long-anticipated the possibility of this infestation’s approach, and we have taken steps to address many of the consequences that may result from it. Unfortunately, at this time, there are no available means to eliminate zebra mussels once they arrive in a body of water.