Keystone WILD! Notes

WINTER 2007-2008

zebra mussels found in cowanesque lake


Biologists this summer discovered zebra mussels in Cowanesque Lake, Tioga County, marking the first time the exotic species has been found in Pennsylvania’s portion of the Susquehanna River watershed.

Zebra mussels threaten aquatic ecosystems because of their ability to filter about a quart of water per day. While water clarity is improved during this process, the zebra mussels disrupt the food chain by removing plankton, which supports the existence of native mussels and fish.

zebra mussels
Zebra mussels disrupt the food chain by removing plankton, which supports the existence of native mussels and fish.
(Click on photo to view full-size)


Zebra mussels pose serious threats because of their potential to foul industrial facilities and plug public water supply intakes that draw from infested waters. Invasive species also can interfere with the operation of locks and dams on rivers or damage boat hulls and engines.

The Pennsylvania Zebra Mussel Monitoring Network first discovered the mussels in Cowanesque Reservoir on May 17 as part of a routine monitoring visit. Verification analyses were conducted by the Department of Environmental Protection and Pennsylvania Sea Grant to confirm the species of mussel.

The mussels have been found in New York’s portion of the Susquehanna watershed since 2000.

Zebra mussels are prolific breeders and, because they are not a native species and have few natural predators, controlling and cleaning up after the mussels is difficult, very expensive and generally unsuccessful. The best control is to limit the spread of zebra mussels by cleaning boats and equipment before and after use.

Adult zebra mussels can be found in other Pennsylvania waters, including Lake Erie, the Ohio River and lower portions of the Allegheny and Monongahela rivers. The mussels have also been reported in Edinboro and Sandy lakes in northwestern Pennsylvania, as well as upper French Creek in Crawford County.

The zebra mussel is native to the Black and Caspian seas region of Eastern Europe. They were introduced in the United States around 1986 when ocean-going ships released infested ballast water into the lower Great Lakes.

The Pennsylvania Zebra Mussel Monitoring Network is sponsored by the DEP, Pennsylvania Sea Grant and the National Oceanic and Atmospheric Administration’s Coastal Zone Management Program to help slow the spread of invasive mussels in the commonwealth’s rivers, streams and lakes.


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