Biologists discovered 20 young zebra mussels in waters near Havre de Grace this month, according to a statement from Maryland's Department of Natural Resources (DNR).

DNR said that its crew was pulling buoys from the water by Havre de Grace for winter storage when members noticed zebra mussels, the invasive mollusk characterized by yellow and brownish stripes, attached to concrete anchor blocks nearby.

“We know that these mussels are from this year’s spawn since these buoys and anchors were deployed this spring,” Matt Ashton, a DNR biologist and mussel expert who helped collect the mussels, said in a prepared statement.

Biologists plan to check the Havre de Grace and other buoys annually to monitor zebra mussels in the upper Chesapeake, Ashton said.

Zebra mussels are "aquatic hitchhikers" found in Maryland in 2008 near the Conowingo Dam and at Glen Cove Marina, and their travels could be costly, DNR reports.

“In their wake, zebra mussels cause economic damages in the billions of dollars, killing imperiled native freshwater mussels, and disrupting aquatic ecosystems,” said Ron Klauda, DNR biologist who helped collect the mussels.

Classified by the U.S. Fish and Wildlife Service as an exotic or invasive species, the zebra mussel attaches to organisms, pipes and structures around waterways that can make them resource-depleted and unnavigable. Once one attaches with the threadlike appendages that extend from under its shell, others follow suit and swarm the same object; zebra mussels have sunk buoys by attaching to them in great numbers, according to the Department of the Interior, which tracks their reach across the country.

Nationally, there have been reports of zebra mussels in approximately 25 states.

“We’d rather not have them in Maryland waters, but they’re now established in the Susquehanna," Klauda said. "So far, that’s the only place in the state where we’re convinced they’ve taken hold. We’re asking our boaters and anglers to be vigilant and help prevent their spread to other waters."

Boaters and anglers can help prevent the spread of zebra mussels by following these DNR-issued precautions before launching and leaving the area:

• Remove aquatic plants and mud from boats, motors, and trailers, then put debris in trash.
• Drain water from boat motors, bilges, live wells, bait buckets and coolers before leaving.
• Trash unused live bait on land, far from the river or bay.
• 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 for two to five days between outings.
• Limit boating from the Susquehanna and upper Chesapeake to other water bodies in Maryland where zebra mussels haven’t invaded.

DNR encourages people who live and work on the water to look out for zebra mussels and call 410-260-8615 if they find anything suspicious. If people see a zebra mussel, officials ask that they bag it and freeze it, then call the number above.