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Invasive Zebra Mussels Spread Downstream Toward Baltimore Harbor

zebramusselsDNR Calls on Public to Report Suspected Sightings

The Maryland Department of Natural Resources (DNR) recently confirmed the presence of zebra mussels (Dreissena polymporha) in tributaries of the upper Western Shore near Middle River in Baltimore County.  On August 17, 2015, a waterman alerted DNR Biologist Brenda Davis of small zebra mussels fouling their crab gear off the Gunpowder, Bush and Middle Rivers. The next day, DNR Fisheries Habitat and Ecosystem Program biologists found numerous mussels in aquatic vegetation while trawling Middle River.

“Zebra mussels are an aggressive invasive species and reproduce at a very prolific rate, outcompeting native species for needed resources,” said Matt Ashton, a DNR biologist and mussel expert. “These mussels quickly overtake and cover all available areas to such an extent that they can clog water intake structures, boats, moorings, ropes, fishing lines, traps, and even dams and power plants. Their migration further south toward Baltimore may pose a serious economic and environmental threat to the bay and its inhabitants.”

Past monitoring suggested that zebra mussels had not spread beyond the Susquehanna Flats. However, heavy rainfall in the late spring has led to lower than average salinity in the upper and middle Chesapeake Bay, potentially allowing zebra mussels to spread into habitat where they would normally not survive. It is not yet known if zebra mussels will persist in these upper Chesapeake Bay tributaries as salinity levels increase around the Baltimore area.

Recreational boaters, anglers, waterman, and others can help prevent the spread of zebra mussels to other Maryland waters by taking these simple, proven precautions:

  • Remove all aquatic plants and mud from boats, motors and trailers; and put the debris in trash containers.
  • Drain river water from boat motors, bilges, live wells, bait buckets and coolers before leaving to prevent these aquatic hitchhikers from riding along.
  • Dispose of unused live bait on shore, far from the river or Bay, or in trash containers.
  • Rinse boats, motors, trailers, live wells, bait buckets, coolers and scuba gear with high pressure or hot water between trips to different water bodies.
  • Dry everything at least two days, and preferably five days, between outings.
  • Limit boating from place to place ─ particularly between the Susquehanna and Middle River to other water bodies in Maryland ─ where zebra mussels haven’t invaded.

For more information on zebra mussels is available at, including a fact sheet and reporting form. DNR asks citizens, to report any suspected sightings to