Zebra Mussel

Zebra Mussel: Invader that shook federal policy

© Amy Benson, U.S. Geological Survey, Bugwood.org

Scientific name: Dreissena polymorpha.

Origin: Vicinity of Caspian Sea, Russia. Later spread through Europe.

When discovered in North America: 1988.

Where: Lake St. Clair—a small body of water connecting Lake Huron and Lake Erie—near Detroit, Michigan. Within a year spread throughout Lake Erie.

Latest distribution:
All Great Lakes and major eastern North American river systems. Now invading inland lakes throughout northeastern and central United States. Sightings in southern California, Virginia. See other U.S. Geological Survey zebra mussel distribution maps. There is great concern that zebra mussels may be unintentionally transported into Western waters by one of the tens of thousands of boaters expected to participate in the Lewis and Clark Bicentennial in 2003.

Responsible for U.S. introduction: Transatlantic ships. A cargo ship takes on ballast water in one port and dumps it in another, along with any number of aquatic species. Zebra mussels arrived in ballast water probably taken from a European freshwater port.

Could it have been avoided?: Although scientists had quietly predicted the zebra mussel was a prime candidate for invading North American waters, with no government agency clearly in charge of aquatic pest surveillance, the warnings went unnoticed. After the invasion, lawyers searched, but found no one to sue.

Pathways of distribution: As microscopic larvae, transported to new waters in boat and ship wells, bilgewater, ballast water, and bait buckets. As adults, transported to new waters while attached to hulls of boats, aquatic equipment, and aquatic vegetation.

© James F. Lubner, University of Wisconsin Sea Grant Institute, Bugwood.org

Shopping cart is completely encrusted after just a few months in zebra mussel infested water.

Impacts: Unlike native freshwater bivalves, which prefer to burrow into mud, the zebra mussel latches onto any hard surface it finds—rocks, pipes, boat hulls, other bivalves, even sunken shopping carts. A million can cover one square meter. Their shells have trashed Great Lakes beaches. Great Lakes facilities using surface water spent $120 million for zebra mussel monitoring and control between 1989-1994, according to the results of a survey in 1995 by an Ohio Sea Grant researcher named Leroy Hushak. Zebra mussels have been estimated to cost $750 million to $1 billion by the turn of the century.1

Zebra mussels are rearranging the ecosystems they invade, too. They filter vast amounts of water to consume microscopic phytoplankton. Although the filtering improves water clarity, it leaves less food for other organisms, with effects rippling through food webs. Native mollusks have disappeared from Lake St. Clair. Fishery populations in the Great Lakes are also being affected, though it will take more years to sort out the impact of zebra mussels from other assaults. Diving ducks such as scaup do feed on the mussels but have hardly made a dent in zebra mussel populations. These predators “take huge numbers, but it’s against a background of astronomical numbers,” says one of the world’s preeminent aquatic biologists, James T. Carlton of Williams College.

Policy reaction: The zebra mussel remains the poster species for invasive species law. Its arrival led to passage of the Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990, which became the National Invasive Species Act of 1996. Among its provisions, the law directs the Coast Guard to ensure that ships headed for the Great Lakes exchange their freshwater ballast with salt water. NISA is due for reauthorization this year.

What YOU can do2:
Take precautions to ensure that you aren’t transporting zebra mussels or other pests to unaffected waters. Before leaving any body of fresh water, inspect your boat’s hull, motor, and trailer, and be sure to remove all plants and animals. Very young zebra mussels look like black pepper and feel like sandpaper on the boat. Afterwards, on land away from fresh water, drain your motor, live well, and bilge. Rinse your boat, trailer, and equipment. High pressure hot water is best, but a garden hose will work. Air dry your boat and equipment for as long as possible. At least five days is optimal since zebra mussels can live in dry conditions for several days.

Bait buckets can harbor zebra mussels. Never release live bait into a body of water or transport aquatic animals or plants from one body of water to another. Empty your bait bucket on land away from water.

For details and more guidelines on what YOU can do to prevent and control invasive species, go to: What You Can Do to Prevent Species Invasions.


  1. Pers. comm. from C. R. O’Neill in Carlton, J.T. 2001. Introduced Species in U.S. Coastal Waters: Environmental Impacts and Management Priorities. Pew Oceans Commission, Arlington, VA.
  2. Adapted from a press packet from the 100th Meridian Initiative/Pacific States Marine Fisheries Commission. For more information on their efforts to protect western waters from zebra mussels, visit www.protectyourwaters.net or www.100thmeridian.org.

Last Revised: May 2002