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Everything You Need to Know about Zebra Mussels

Posted on March 26 2019

Everything You Need to Know about Zebra Mussels

First up, what are zebra mussels?

Zebra Mussels and Quagga Mussels are small freshwater molluscs originating from the Ponto–Caspian region of Eastern Europe. Zebra mussels are filter feeders. This means that they filter and eat algae and other particles from the water.

Unlike nearly all other freshwater molluscs (such as clams and snails) Zebra Mussels and Quagga Mussels grow while attached to hard surfaces such as rocks and plants and unfortunately, boats, motors and water intakes. One of their other unique qualities is the density in which they congregate. For example, it is common to find more than 10,000 individual mussels per square metre on hard surfaces.

A single Zebra Mussel can filter one quart of water per day while feeding primarily on algae. They live underwater, attached to natural and manmade substrates such as rocks, wood, plants, native mussels, pipes, docks, boat lifts, swim rafts, moored watercraft, and other debris. A female can produce 100,000 to 500,000 eggs per year. Fertilized eggs develop into microscopic, free-living larvae, called "veligers," that form shells. After two to three weeks, the veligers settle and attach to a firm surface using tiny fibers called byssal threads.


When did zebra mussels arrive in Canada?

Zebra Mussels were first detected in Lake Erie in 1986. Within a few years, they had spread all around Lake Erie and into the rest of the Great Lakes. Within ten years, Zebra Mussels had travelled from the Great Lakes to smaller inland lakes, through the Mississippi drainage to the Gulf of Mexico. They now occupy over 800 lakes, mostly in eastern North America. Unlike the Zebra Mussel, Quagga Mussels are found to be limited to the southern Great Lakes; Lake Ontario, Michigan, Huron and Erie. They have also been found in the St. Lawrence River and north to Quebec city.

Regulatory Classification

The zebra mussel (Dreissena polymorpha) is a prohibited invasive species, which means it is unlawful (a misdemeanor) to possess, import, purchase, transport, or introduce this species except under a permit for disposal, control, research, or education.

Do we know how zebra mussels first arrived in Manitoba?

We will likely never know for sure. The current weight of evidence, however, suggests that they came in via the Red River, either in the form of a veliger (the planktonic larva of many kinds of sea snails and freshwater snails) or as adults floating down the river, attached to debris or plant material. It is also possible that they arrived overland attached to a boat or other equipment being transported from an invaded habitat. The closest invaded habitats are in North Dakota and Minnesota.

How widely have zebra mussels invaded freshwater bodies in Manitoba?

They have been found in the Red River in several locations, in the south basin of Lake Winnipeg (where they are rapidly expanding) and the north basin of Lake Winnipeg near George Island. There was a veliger detected in Cedar Lake, immediately west of Lake Winnipeg’s north basin.

In June 2017, a “suspect mussel” was found in Singush Lake in Duck Mountain Provincial Park. (It is considered suspect because it was small, dry and damaged; while experts could not identify the specimen as a Zebra Mussel, DNA analysis came back positive. However, there is a concern the sample may have been contaminated from the lab procedures.)

In December 2017, environmental DNA evidence of Zebra Mussels were found in Whirlpool Lake in Riding Mountain National Park. Environmental DNA are microscopic genetic traces that an organism leaves behind as it moves through an environment. The lake and campground area are now closed until further notice as a precautionary measure. It is possible that zebra mussels are present in other locations but have not yet been detected.


What effects will zebra mussels have on aquatic ecosystems in Manitoba?

The short answer is that this will depend on the size of the zebra mussel populations that establish themselves. In some places, zebra mussels are able to filter the entire volume of water within a lake within a few days, removing algae and other particles from the water. The reduction of algae (i.e., food) has led to declines in fauna (i.e., insects and fish) in some lakes. Because the mussels live at the lake bottom, this is also where they release their nutrient-rich waste products that can stimulate plant growth at the lake edges. In some cases, like the Laurentian Great Lakes, zebra mussels have caused large shoreline algal blooms that were unsightly, released noxious smells and promoted high bacterial growth when decomposing.

 This invasive species can cause recreational, economic, and ecological damage—changing how residents and visitors use and enjoy any water body.

Zebra mussel impacts:

  • Encrust equipment, such as boat motors and hulls, which reduces performance and efficiency and is costly to clean and repair.
  • Swimmers and pets can cut their feet on zebra mussels attached to rocks, docks, swim rafts and ladders.
  • Create a costly problem for power plants, cities and residents when they clog water intakes.
  • Filter tiny food particles out of the water, which can reduce available food for larval fish and other animals and can increase aquatic plant growth as a result of increased water clarity.
  • Attach to and kill native mussels.


What will we likely see in Lake Winnipeg specifically?

The limiting factor for Lake Winnipeg will be the availability of hard surfaces (rocky lake bottom, docks, etc.). We should expect most rocky surfaces in the southern basin to be completely covered in zebra mussels within a few years. This is also true for docks, watercraft, water intakes and other infrastructure that are left in the lake for long periods of time. The implications of zebra mussels for the ecology and fisheries of Lake Winnipeg are going to take longer to appreciate and will require careful monitoring.

What did Manitoba’s government do to try and stop zebra mussels from establishing themselves in Lake Winnipeg? Did it work?

In May 2014, the government of Manitoba temporarily closed four harbors where Zebra Mussels had been found in order to treat them with liquid potash, a substance harmless to humans but lethal to mussels. The experimental action was an attempt to eradicate the unwanted mollusks before they could further establish themselves in the lake.

Although the potash treatment did succeed in killing Zebra Mussel populations in Winnipeg Beach, Gimli, Arnes and Balsam Bay harbours, both adult mussels and veligers have since been detected throughout the lake’s south basin, as well as in the Red River, and the harbours have been re-invaded. In late October 2015, Manitoba Conservation and Water Stewardship reported zebra mussels are also now present in the north basin of Lake Winnipeg.


In the meantime, what can the public and other lake users do?

It’s hard to imagine that something so small can cause so much damage! Zebra mussels remain one of the most notorious invasive species in North America, causing millions of dollars in damages to utility pipes annually, and altering natural habitats by competing with fish for food. All lakes in proximity to the Lake Winnipeg watershed are now at risk of being invaded, so the most important action that individuals can take is to ensure that they thoroughly clean items (boats, boat trailers, buoys, etc.) removed from Lake Winnipeg before placing them in another water body. Second, boat hulls, motors, water intakes and other “in lake” infrastructure will likely require increased maintenance. Third, if you live or access areas of the lake where adult zebra mussels are found, you should be cautious and wear correct footwear in the water. The shells of the mussels can be quite sharp when stepped on and can easily cut exposed skin.

People spread zebra mussels primarily through the movement of water-related equipment. Mussels attach to boats, docks, swim rafts and boat lifts. They can also attach to aquatic plants. Adult mussels can survive out of water – less than five days in dry conditions, but up to 21 days in very wet conditions (such as inside dock/lift pipes). Microscopic larvae (veligers) can survive in water contained in bait buckets, live wells, bilge areas, ballast tanks, motors and other water-containing devices.

Whether or not a lake is listed as infested, you are required to:

  • Inspect your boat and equipment for any invasive species.
  • Clean watercraft of all aquatic plants and prohibited invasive species.
  • Drain all water by removing drain plugs and keeping them out during transport.
  • Dispose of unwanted bait in the trash.
  • Dry docks, lifts, swim rafts and other equipment for at least 21 days before placing equipment into another water body. 


  1. Inspect your boat and remove debris before launching into the water. Your boat should be clean and dry and contain no mussels. It should also be free of plants, mud, and standing water as these elements could contain small mussels or larvae.


  • Pay attention to areas like the hull, anchor, dock lines, live wells, bilge, and the motor.
  • Be careful not to empty standing water into another body of water as this could cause contamination. Towel dry any residual wetness left on your watercraft.


  1. Drain all water after boating and before leaving the shore. Empty the bilge, live wells, motor, and all water-intake systems. Once you’re away from all bodies of water, do a more thorough cleaning of all areas of your watercraft that came into contact with the water.


  1. Remove visible species and plants and dispose in the trash. Never transport to or dispose in another location because this can contribute to new infestations. Double-check problem areas to make sure you don't miss any mussels. This includes the hull, anchor, props, and dock lines. Don’t forget to check less-obvious places like the boat trailer, rollers, bunks, and wheel axles.


  1. Dispose bait and empty bait buckets in an approved location. Empty all water and leftover bait onto dry land, away from the water, or in the trash. Some locations offer special bags for this purpose. Bait can carry larvae which may infect uncontaminated water. So can dipping bait buckets from place to place.


Decontaminating Your Boat

  1. Visit a Watercraft Inspection Station to get help from a professional. A trained inspector will thoroughly check your boat and equipment and will decontaminate as necessary.
  • Do a quick check of your state’s Fish & Wildlife Department website to confirm locations, hours, and fees associated with the inspection.
  • Some localities perform these inspections as a courtesy, however, many states charge a fee for this service. The fee ranges from $5 to over $100, depending on the size and type of watercraft.
  • Some states offer a yearly permit to allow for multiple inspections and/or locations.


  1. Hose your watercraft with hot, low-pressure water to kill the mussels. If you are unable to visit an inspection station, you can decontaminate on your own. The water temperature should be at least 140 °F (60 °C). Make sure you keep the nozzle within 4 inches (10 cm) from the surface and allow contact for at least ten seconds. Avoid using chemicals during this process. They aren’t typically effective in killing zebra mussels and may cause damage to your boat and/or water equipment.


  1. Use a pressure washer to remove any mussels that are still attached. The pressure should be set to 3,000 - 3,500 psi. Keep the nozzle at least 16 inches (41 cm) away from the surface to avoid damage to your watercraft.


  1. Allow your watercraft and equipment to dry completely. Thoroughly drying all internal and external parts of the watercraft is crucial. Leave doors and lids open, and towel dry any residual water. Your watercraft should dry for at least five days in the hot summer heat. This can increase up to 30 days in milder fall and spring weather and/or depending on the temperature and humidity of your location.


  1. Expose watercraft to extremely cold temperatures during winter months. Alternatively, for areas with colder temperatures, storing the watercraft below 14°F for three consecutive days is also effective in killing mussels.




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