For the first time, Maryland waters have been invaded by an alien mussel capable of fouling public water systems, destroying native aquatic life and causing millions of dollars in damage.
A single zebra mussel was scooped from inside a water intake pipe upstream from the Conowingo Dam that spans Harford and Cecil counties by a fish survey team on the Susquehanna River. The mussel, about a half-inch in size, was sent to a Pennsylvania laboratory for positive identification.
"Finding just one doesn't make sense," said Jonathan McKnight, an invasive species expert with the Maryland Department of Natural Resources. "When they show up, they show up with a vengeance."
McKnight says DNR staff will post signs at Susquehanna River launching ramps to remind boaters and anglers to report any sightings and to scrub their vessels and equipment before moving them to prevent unwanted hitchhikers.
"At this point, all we can do is be vigilant and hope the public will be vigilant, too," said McKnight, chairman of the Mid-Atlantic Panel on Aquatic Invasive Species. "But if we find there's a population in Conowingo, then we have a problem."
The zebra mussel is native to Europe's Black and Caspian seas. The mussels entered the Great Lakes in the mid-1980s in the ballast water of an oceangoing freighter. Since then, the mollusks have spread to waters that border or cut through more than 20 states, Quebec and Ontario. This month, they were discovered in a high-mountain lake in Utah.
Zebra mussels reproduce rapidly and attach to structures and each other, building dense layers up to a foot thick. They spread by traveling in the bottom of boats or by attaching to propellers, bilges and anchors or floating docks.
In addition to clogging reservoir ducts and hydroelectric dam intake pipes, the mussels upset the balance of nature by removing nutrients needed by other species.
Sarah Whitney, associate director of Pennsylvania Sea Grant, said baby mussels might not be visible so it's important for boaters and anglers to let equipment air-dry for five days before moving it to another body of water.
"The piece that's critical to all of this is prevention, because the cost of control is so expensive," she said.
The federal government estimates zebra mussel control programs cost about $5 billion each year. Four years ago, it cost Virginia $150,000 to clear a single quarry.
Maryland officials began preparing a defense more than a decade ago, spending millions of dollars to establish monitoring sites on waterways and building defenses at reservoirs.
The Baltimore Department of Public Works spent $3.6 million in the mid-1990s to install equipment to prevent the mussels from building up in water intake pipes at Liberty and Loch Raven reservoirs and the Susquehanna River. Other controls were installed at Prettyboy Reservoir.
But a new sense of urgency emerged in 2002, when zebra mussels were detected in the Chesapeake Bay watershed in upstate New York. Waterways with transient traffic such as Deep Creek Lake and Jennings Randolph Reservoir in Western Maryland and the upper Susquehanna were considered likely entry points.