What are Zebra Mussels?
Zebra mussels (Dreissena Polymorpha) are small, freshwater bi-valve mollusks (relatives to clams and oysters) that are triangular in shape with an obvious ridge between the side and bottom. The zebra mussel gets its name from the black (or dark brown) and white striped markings that appear on its shell.
How To Identify the Zebra Mussel
Zebra mussels look like small clams with a yellowish or brownish D–shaped shell, usually with both dark and light-colored stripes, which can vary in intensity.
Zebra mussels can be up to two inches long, but most are under one inch in length. Zebra mussels grow in clusters containing numerous individuals and are generally found in algae-rich, shallow water (6 - 30 feet).
Zebra mussels are the ONLY freshwater mollusk that can firmly attach itself to solid objects, including submerged rocks, dock pilings, boat hulls, water intake pipes, etc. They attach using byssal cords, seen in the photo here.
Zebra Mussels and Lake George
Zebra mussels were discovered in Lake George’s southern basin in December 1999. Archeologists discovered a colony of adult Zebra Mussels near the village walkway along the southern shore. This was the first confirmed incidence of adult zebra mussels in the Lake. (Zebra mussels in the microscopic larvae stage (veligers) had previously been found.) A Zebra mussel task force was formed in 2000 to address the problem. Today, this task force exists as the Lake George Invasive Species Task Force, and addresses all invasive species. Click here or on the photo at right to see a map of all known locations of zebra mussels.
The zebra mussel poses a multi-billion dollar threat to the Lake George region. Outdoor recreation, tourism, property values and the municipal water supply are threatened. Zebra mussels can foul boats and boat engines, foul beaches with washed-up remains, clog water intake pipes, alter water quality and affect the overall lake ecosystem. Adult zebra mussels can be transported by attaching to boat hulls, engines and anchors. Zebra Mussel larvae can be carried in the water of engine cooling systems, bilges, live wells and bait buckets.
What to Do if You Find Zebra Mussels in Lake George
Contact us IMMEDIATELY. Note the date and precise location where the zebra mussel was found. Take the zebra mussel (if possible) with you and store it in rubbing alcohol.
What you can do to help
- Learn all you can about the Zebra Mussel. (How it spreads, how to identify it, and the threat it poses.) Share this information with others.
- When Boating Arrive Clean, Drained, and Dry.
- When enjoying the Lake, look on rocks, dock frames, your boat hull, anchors, buoys, chains, etc. Zebra Mussels like to attach to hard surfaces.
Click on the interactive map above to see a progression of zebra mussel infestations in the US over the years.
Where are Zebra Mussels From?
Zebra mussels are native to the Caspian, Black and Aral Seas in Eastern Europe and Western Asia. The Zebra Mussel was first identified in the United States in the waters of Lake St. Clair in June of 1988.
It is believed that Zebra Mussels were introduced into North America through the emptying of ballast water from commercial transatlantic ships into the Great Lakes.
Cargo ships carry significant amounts of ballast water to stabilize the vessels during transoceanic crossings. When ballast tanks are filled, many forms of aquatic life in the source water are drawn into the tanks. Once in ballast tanks, organisms can be transported to other areas and subsequently discharged into waters at foreign ports.
How Do Zebra Mussels Spread?
Female zebra mussels can each produce up to one million veligers (the microscopic larvae stage). The veligers float in the water; If they are unable to find a hard surface, the veligers will soon die.
Veligers can be spread through a variety of methods including: water currents, bait and hatchery stocking activities, anglers’ bait bucket water, recreational boat engine cooling water and even scuba gear.
Adult zebra mussels can spread by “hitchhiking” on organisms such as crayfish or by attaching to boat hulls trailered from one body of water to another.
Media Credit: Steve Krynock, Michigan Sea Grant, Bugwood.org
Biological & Ecological Impacts
Zebra Mussels can cause a variety of problems including:
- Zebra mussels are filter feeders that consume large portions of the microscopic plants and animals that form the base of the food web. The removal of significant amounts of phytoplankton from the water can cause a shift in native species and a disruption of the ecological balance of a lake. Increased water transparency may result in an increase in rooted aquatic vegetation, including nuisance species such as Eurasian watermilfoil.
- Zebra mussels can reduce native mussel populations by attaching to them, hindering their movement, feeding and respiration.
- Zebra mussels also may contain high concentrations of toxic materials that will harm or kill the fish and wildlife that consume them.
- Decaying mussels wash ashore littering beaches and creating a noxious odor.
Image Credit: Randy Westbrooks, USGS, Bugwood.org
Residential, Industrial and Recreational Impacts
- Zebra mussels can clog the large-scale raw water intake pipes of municipal drinking water plants, and the small-scale water intake pipes of private homes and cottages, causing lost pumping ability, obstructed valves, obnoxious smells from decaying mussel flesh, increased corrosion of cast iron pipes, and safety hazards if sprinkler or hydrant systems are clogged and fail to deliver fire-fighting water.
- Zebra mussels can rapidly colonize and foul docks, break walls, boat bottoms, buoys and engine out-drives.
- Swimming areas become abandoned due to sharp-edged shells washing up on shore from storms, colonization on rocks near the shoreline, and noxious odors from decomposition of mussels.
- Boats may overheat due to zebra mussels blocking engine cooling water intakes. Mussels attached to hulls can increase drag, therefore increasing fuel consumption.
- Historic, sunken ships and artifacts may become completely obscured by zebra mussel colonies growing on them.
Image credit: Craig Czarnecki, Michigan Sea Grant, Bugwood.org