Zebra Mussel

(Dreissena polymorpha)

Zebra mussels are small mollusks native to the Caspian Sea, Black Sea, and the Sea of Azov. They were accidentally introduced into the Great Lakes in the mid-1980s, most likely as larvae (also known as veligers) in discharged ballast water of commercial cargo ships and soon spread throughout Wisconsin through recreational activities. Zebra mussels can hitchhike on boats and trailers, allowing them to travel long distances between waterbodies. They may also be attached to any unremoved plants or hiding in the mud. Adults can survive outside of water for several days in moist conditions. Zebra mussel veligers can also be carried to other waterbodies by currents or by residual water left in boating and fishing equipment (e.g., live wells, bilge pumps, engine cooling systems, bait buckets).

Overview map of zebra mussel classification in WI — Restricted (orange) counties

Other names for this animal include:

Scientific names: Dreissena polymorpha

Classification in Wisconsin: Restricted

Ecological and Socio-economic Impacts

Zebra mussels are very effective filter feeders and can impact plankton and algae populations. While their presence can lead to a temporary increase in water clarity, they may deplete the food supply for fish and other aquatic organisms.
Zebra mussels avoid consuming blue-green algae, potentially increasing the likelihood of toxic harmful algal blooms.
Zebra mussels can attach to the shells of native mussels, effectively smothering them.
Zebra mussels can clog pipes, damage recreational equipment, and cut swimmers’ bare feet. Removing them from docks and other hard structures can be very difficult and time-consuming.

Identification

Zebra mussels have a distinctive “D”-shaped shell with alternating dark- and light-colored zigzag stripes, similar to a zebra. Adult zebra mussels are typically 1/8-inch to 2-inch long. They are often found attached to hard surfaces, like rocks, docks, shells, and wood, but can attach to any solid surface, including submerged aquatic plants, native invertebrates, and each other.

Similar species: Quagga mussel, sheepnose mussel

Distribution

See the reported locations of this species in Wisconsin on the Aquatic Species Tracking pages.

Do you know of additional populations? Send us a report.

Control

Prevention: The best way to keep a lake free of zebra mussels is to prevent their establishment. Wisconsin’s invasive species law prohibits the transport of aquatic plants, live animals and water from a waterbody, with some exceptions for bait.

Before leaving the boat launch, conduct the following actions required by law:

Inspect and remove aquatic plants and animals from boats and equipment.
Drain all water from the boat and equipment.

Before entering another waterbody, conduct one of the following:

Spray the boat and equipment with high-pressure hot water.
Spray the boat and equipment with a ~500 ppm bleach solution (approximately 2 ½ tablespoons of household bleach (5.25% sodium hypochlorite) in 1 gallon of water) for 10 minutes.
Allow the boat and equipment to dry out of water for at least 5 days.

Mechanical: Physical control options include benthic mats, manual removal, water level drawdown, and dredging. They may be effective at controlling zebra mussels at a localized site or structure; however, they are often expensive and can have negative impacts on native plants and animals. In addition, some of these physical control options may also require an approved permit from the DNR Waterways program.

Chemical: Several pesticidal control options have been developed, including copper compounds (EarthTec® QZ), the bacterium Pseudomonas fluorescens strain CL145A (Zequanox®), and potassium chloride (potash). However, due to the lack of documented long-term control efficacy, as well as the potential risk to non-target species, the Wisconsin Department of Natural Resources does not currently support the use of pesticides to control zebra mussels in lakes or rivers. Any product which claims to kill, control, repel, mitigate, or prevent zebra mussels would be considered a pesticide and must be registered with the Wisconsin Department of Agriculture, Trade, and Consumer Protection (DATCP). In addition, the proposed use of any pesticidal product in a Wisconsin waterbody would also require an approved Chapter NR 107 permit for the control of aquatic organisms.

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