HAVRE DE GRACE, Md. (WJZ)—An aquatic hitchhiker, which caused millions in damage, is being spotted in Maryland in the upper Chesapeake Bay.

As Mike Schuh reports, the zebra mussels were pulled up near Havre de Grace.

Twenty-five years ago they were first found in the Great Lakes. Though tiny, they grow in clusters causing billions in damage.

“They have a lot of economic damages,” said Matt Ashton, Maryland Department of Natural Resources biologist. “They can foul water intake pipes for drinking water supply, power plant cooling. They interfere with recreational boating. They can become attached to their boats and their docks.”

Now found in 20 states, the problem in Maryland is getting worse.

“On three of the six buoys on the upper bay we found about six zebra mussels on the anchor chain, on the anchor,” Ashton said.

Since there’s no way to get rid of them, there are fears about what happens next.

“Really they can cause whole scale changes in the ecosystem,” Ashton said.

Elsewhere, shad and striped bass populations have declined while causing an increase in bacteria and trash fish.

“They’re spreading downstream,” Ashton said.

Brought here by ocean freighters but thought to be transplanted by small recreational boats.

The state asks boaters to wash and clean their craft and never to pump out bilge water from one body of water to the next.

If you find a zebra mussel, DNR asks you to bag it and freeze it and give them a call.