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Government of Manitoba
Conservation and Water Stewardship
Aquatic Invasive Species

Zebra Mussels (Dreissena polymorpha)

Zebra mussels are small non-native, clam-like, aquatic animals that are a significant environmental and economic concern to Manitoba. Native to Eastern Europe and Western Asia, zebra mussels have caused millions of dollars in damage to the Laurentian Great Lakes area and have cost the North American economy billions of dollars to control.

A Zebra Mussel
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Zebra Mussel impact:
  • Aggressively invade new areas and reproduce quickly. A female zebra mussel can produce upwards of one million eggs per year.
  • Colonize almost any hard surface including watercraft hulls, motors or anything immersed in the water and can interfere with engine cooling systems.
  • Negatively impact essential power and water-based infrastructures by obstructing water-intake pipes, such as, for public drinking water supply and cooling systems.
  • Threaten native fish and wildlife by reducing species of algae and microscopic aquatic animals that are important for the food chain. Zebra mussels attach to native mussels and crayfish making it hard to them to survive.
  • Costly nuisance to boaters, commercial fishers, anglers, and beach-goers. Zebra mussels can reduce recreational potential by littering beaches with numerous sharp shells and producing foul odours from decaying, dead zebra mussels. They can clog watercraft water intake pipes causing costly repairs

Zebra mussels colonizing a native clam making feeding difficult
Zebra mussels colonizing a native clam making feeding difficult.
Photo credit: Randy Westbrooks USGS Budwood.org

How to identify an adult Zebra Mussel:
  • Usually 1 to 3 cm (0.4 - 1.2 inches) long.
  • Triangular, or "D"- shaped shell.
  • Most have light and dark brown bands on shells (Figure 1).
  • Adult shells have very strong tufts of hair-like filaments, called byssal threads.
  • Usually grow in clusters containing numerous individuals.
  • Zebra Mussels and Quagga Mussels are the ONLY freshwater mussels that firmly attaches themself to solid objects, including rocks, watercraft hulls etc. Native mussels will bury into soft substrates on lake and river bottoms.
  • Unlike adults, young zebra mussels, called veligers, in their larval stage are free-swimming and microscopic; they are difficult to see with the naked eye.

History of Zebra Mussels in the Red River Basin

On July 1, 2010, microscopic, larval zebra mussels were found for the first time in the Red River. The mussels were found where the Ottertail River empties into the Red River at Wahpeton, North Dakota and Breckenridge, Minnesota. This is the first time zebra mussels have been reported in North Dakota.

Previous to this, live zebra mussels were found in (Big) Pelican Lake, Minnesota approximately 50 kilometres south east of Fargo, North Dakota and Moorhead, Minnesota in September 2009. This was the first known incidence of zebra mussels in the Red River watershed.

Zebra mussels were likely transported into Pelican Lake by unsuspecting boaters who previously launched their boat in zebra mussel-infested waters.

Waters from Pelican Lake flow into Pelican River, which flows into the Ottertail River near Fergus Falls, Minnesota and then into the Red River at Breckenridge, Minnesota. All water that originates in the Red River watershed eventually flows into Manitoba and Lake Winnipeg. No adult (with shells) zebra mussels have been identified in the U.S. portion of the Red River to date.

Since the initial introduction in North America in 1985, zebra mussels have steadily invaded south-eastern Canada and the majority of the eastern half of the United States. They have infested the Laurentian Great Lakes, and the Hudson and the Mississippi drainage areas.  Zebra mussels are also found in parts of California, Arizona, Nevada, Utah, Colorado and Texas.

How can Zebra Mussels spread?

Each year thousands of tourists, recreational boaters and anglers flock to Manitoba's numerous lakes and rivers. With this comes the threat of transporting zebra mussels overland to new areas on watercraft, trailers and gear.

Because they can close their shell, adult zebra mussels are able to survive out of water up to 7 to 30 days depending on temperature and humidity. As a result, they can easily be transported long distances on firm surfaces such as:

  • watercraft,
  • motors,
  • fishing nets,
  • aquatic plants/debris,
  • scuba equipment,
  • scientific sampling equipment,
  • float plane pontoons, and
  • related equipment.

Young, microscopic zebra mussels can die quickly out of water. However they can easily survive and be transported to new un-invaded areas in almost any remaining water found in (for example):

  • livewells,
  • motor compartment,
  • bait buckets, and / or
  • bilge, and/ or
  • pontoons

Once introduced into a new area, young (larval, free-swimming) Zebra Mussel veligers can spread by:

  • inter-connecting waterways
  • illegal bait-bucket transfers
  • watercraft bilge or livewell discharges
  • float plane pontoons and/or
  • the general movement of water from one place to another

Invaded Waters

Updated: July 10, 2015

Zebra Mussels are located in:

How you can help

Help protect Manitoba's waters and resources.

Before launching any watercraft or water-based equipment into any Manitoban waterbody such as a lake, river or wetland, and before leaving the boat launch:

CLEAN watercraft, trailer, all water-based equipment.

  • Remove all detectable aquatic plants, aquatic invasive species and mud.
  • Rinse using all surfaces that came into contact with the water with hot water - preferably 50°C (120°F) or hotter - to kill any AIS including Zebra Mussels. Use high pressure to remove any attached mussels. Young mussels attaching to surfaces feels like sandpaper.  
  • Inspect drain holes, speedometer brackets, motors, propellers, and other difficult to clean areas, including the trailer and vehicle as Zebra Mussel like to hide in recessed of hard to access areas.


Common places where aquatic invasive species can be found on boat, trailer and vehicle.

DRAIN all on-board water from the motor, livewell, bilge, ballast tanks and bait buckets. Any hard to completely drain areas should be dried with a dry towel or sponge.

DRY all water-related equipment  and watercraft completely. One option is to leave the water-related equipment and/or watercraft to dry in the hot sun for at least 5 days (if rinsing with hot water is not available). Leave all compartments open to allow drying. Alternatively, dry for 8 consecutive days in the spring/fall or 3 days of exposure to constant freezing temperatures (-10°C or lower).

  • Young zebra mussels (veligers) can die quickly out of water; adult zebra mussel (with a shell) can survive up to 7 to 30 days out of water in damp, cool conditions.

DISPOSE of unwanted bait and worms in the trash, and dump bait bucket water on land.
Never release aquarium pets, plants or water into our lakes, rivers or wetlands.

To report a Zebra Mussel or any other AIS from a new location, please take pictures and report a sighting by clicking Report a Aquatic Invasive Species link or call 1-87-STOP AIS-0 (1-877-867-2470).

Aquatic Invasive species (AIS) such as Zebra Mussels, Spiny Waterflea, Rusty Crayfish, and four species of Asian Carp are listed as a schedule attached to the Aquatic Invasive Species Regulation (SOR/2015-0212) under the federal  Fisheries Act. Possessing any of these listed  species in Manitoba is illegal. To learn about the species subject to prohibitions and controls visit the federal regulation site at the Canadian government’s law website.

Background Information:

Where did Zebra Mussels orignate?

Zebra mussels are native to the Caspian, Black and Azov seas of Eastern Europe; they were initially discovered in the Caspian Sea in 1769.

Scientists first discovered a population of zebra mussels in Lake St. Clair in 1988. The zebra mussels were likely transported to North America in the ballast water of a ocean-going ship. This ballast water was then discharged in Lake St. Clair, Ontario, likely in 1985 or 1986.

What are Zebra Mussels?

The zebra mussel (Dreissena polymorpha) is a small aquatic animal that resembles freshwater clams. Zebra mussels grow up to five centimetres (two inches) in length and may live up to five years. Their name originated from the brown and white striped colour of its shell. One mature female zebra mussels can produce up to one million eggs per year depending on water quality conditions.

The eggs hatch into free-swimming microscopic larvae called veligers. During this stage, which lasts for approximately 8 to 33 days, the larvae remain suspended in the water. It is during this stage that the veligers can be transported undetected from lake to lake in bait buckets, live wells, and bilge water.

The distribution of zebra mussels is thought to be controlled mainly by temperature and calcium concentration in the water. They begin laying eggs when water temperatures rise to approximately 12 ºC and continue until it cools below this temperature in the fall. Calcium is required for mussels to develop their hard shell.

Adult zebra mussels can survive out of water, in moist cool conditions, for up to 30 days. They attach to watercraft or other water-related equipment being transported from one body of water to another unless the proper steps are taken to avoid moving them to new areas.

Current Manitoba Regulations:

Zebra mussels are listed on the Manitoba Prohibited Species List (Schedule IX) of the Manitoba Fisheries Regulations under The Fisheries Act.

Manitoba Prohibited Species List
The Water Protection Act



If you think you have encountered an aquatic invasive species, or need further information, please contact:

Manitoba Conservation & Water Stewardship, Fisheries Branch
Box 20, 200 Saulteaux Cres.
Winnipeg, Manitoba, R3J 3W3

Telephone: 204-945-7787
Fax: 204-948-2308
Toll Free: 1-877-867-2470
Email: fish@gov.mb.ca

Related Zebra Mussel Links

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