Sustainable Development

Aquatic Invasive Species

Zebra Mussel Questions and Answers

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 to 2-4 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 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 10 - 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 (with a shell) can survive out of water, in moist, cool conditions, for up to 30 days. Thus they can hitchhike on by attaching to watercraft, water-based aircraft, ORVs or other water-related equipment being transported from one body of water to another.

Where did Zebra Mussels originate?

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 transport ship. This ballast water was then discharged in Lake St. Clair, Ontario, likely in 1985 or 1986 and subsequently introduced Zebra Mussels in the Laurentian Great Lakes.

Can Zebra Mussels veligers (larval-stage) swim upstream?

No. Veligers travel with the water currents; they cannot actively swim. Only humans can move veligers upstream via movement on or in watercraft, water-based aircraft, ORVs and water-related equipment, other vehicles.

Can Zebra Mussel survive out of water?

Yes! This is why Zebra Mussels can be spread to new water bodies. Adult Zebra Mussels (the stage with the shell), can survive 7 to 30 days out of water depending on temperature and humidity.

Veligers, the microscopic larval stage of Zebra Mussels require water to survive and will die out of water.

Thus it is important to remove any Zebra Mussels you can see or feel and drain all the water from all watercraft, trailer, water-based aircraft, ORVs or any water related equipment before it is moved to another water body.

If Zebra Mussels are very small when they first settle how can I tell if they are attached?

Zebra Mussels can start attaching to surfaces within 24 hours. The newly attached Zebra Mussels will feel like sandpaper when you run your hand over the exterior surfaces of objects that have been in the water.

What is the lifespan of a Zebra Mussel?

Zebra Mussels can live for 2-4 years

What happens when they die? Do they remain attached to surfaces?

Zebra Mussels can do both. They can remain attached to a surface when they die and more live Zebra Mussels can grow on top of the dead mussels. They can also detach from the surface when they die as their byssal threads, which are the hair-like tufts they use to attach to a surface, begin to decompose, resulting in them becoming detached from the surface.  Zebra Mussel shells will eventually wash up on shore and foul beaches.

I understand that one of the benefits of the introduction of Zebra Mussels is cleaner or clearer water? Is this true?

Aquatic ecosystems are complex systems and it is often difficult to determine effects on any “one” thing. Human interactions also play a role.

That there are a number of effects that may be directly or indirectly attributed to the introduction of Zebra Mussels. A single Zebra Mussel can filter up to one liter of water a day. In a number of lakes where Zebra Mussels have established, “clearer” or “cleaner” water has resulted because of this high filtering capacity.

While “clearer” or “cleaner” water may be preferred by individuals for aesthetic values, these attributes do not necessarily equate to a healthy ecosystem for those organisms that live in them. The filtering ability also can lead to a shift in the food web and a change in the direction of energy from the open water community to the bottom (or benthic) community. This shift can benefit those species like Freshwater Drum and suckers, which feed on benthic invertebrates, while having a negative impact on those species that survive or feed on species that live in the open water, like Lake Whitefish. 
Other species, like Walleye, have also been affected in some Zebra Mussel infested waters such as the Laurentian Great Lakes. Since Walleye prefer turbid water, an increase in water clarity reduces the amount of preferred habitat resulting in a decrease in numbers and size.

In some lakes there has also been an increase in the frequency of toxic algal blooms. This has been attributed to Zebra Mussels selectively feeding on uni-cellular green algae and avoiding or excreting blue-green algae (the cyanobacteria responsible for the algal blooms). The degree, to which this might occur will depend on other factors within each specific waterbody.

I don’t boat or fish, how can Zebra Mussels affect me?

In Ontario where Zebra Mussels have been established in the Laurentian Great Lakes since the late 80s, their presence of has causes reductions in lake-front property values. Also Zebra Mussels clog water intake pipes and impact water infrastructure leading to increased electricity and water rates because industry, cities and municipalities will pass the extra costs to treat and remove Zebra Mussels onto ratepayers and consumers.

Can humans eat zebra mussels?‎

No. Zebra Mussels are too small and can bio-accumulate toxins which could be detrimental to human health. 

Are there any fines or charges for possessing Zebra Mussels in Manitoba?‎  

Yes. Under the new provincial AIS legislation and the federal Fisheries Act, it is illegal to possess or transport zebra mussels. Penalties for possessing zebra mussels may result in fines or prosecution under either act.

Why not look at cheaper methods of controlling Zebra Mussels like changing fishing regulations to protect natural predators such as Freshwater Drum?

When Zebra Mussels were first detected in Lake Winnipeg in 2013, Manitoba implemented an Early Detection Rapid Response plan. A Science Advisory Committee was formed to provide advice on how best to determine the magnitude and extent of the invasion, interpret data collected, and provide advice on how best to manage the Zebra Mussels. This included potential ways to control the species. Many physical, chemical and biological options were investigated including the role natural predators. While there are species like Freshwater Drum that feed on Zebra Mussels, there is no species known to prevent Zebra Mussels from establishing to nuisance levels. What is most likely to happen is that there will be a new predator-prey relationship within the newly altered Lake Winnipeg aquatic ecosystem. In short, Freshwater Drum may increase in size and abundance as they consume abundant Zebra Mussels, but there is little evidence that they will outstrip their new food source.

The most effective way to control Zebra Mussels is to prevent their spread.

Will Zebra Mussels survive in Manitoba?

Yes, Zebra Mussels will survive. A national risk assessment conducted by the federal department of Fisheries and Oceans shows the majority of Manitoba is at moderate to high risk of being invaded by Zebra Mussels and Quagga Mussels.

How many water bodies in Manitoba are susceptible to Zebra Mussels establishing and surviving when introduced?

The federal department of Fisheries and Oceans did a national risk assessment on the establishment and survival of Zebra Mussel, Quagga Mussels and False Dark Mussels based on calcium levels (see map below). Lake Winnipeg and many water bodies to the south and west of the lake as well as the Nelson River and other lakes and rivers in the Northeast have the ability to sustain moderate to nuisance levels of Zebra Mussels.

What species are prohibited from possession in Manitoba? And where can I find out about the current AIS legislation?

Aquatic Invasive species (AIS) such as Zebra Mussels, Spiny Waterflea, Rusty Crayfish, and four species of Asian Carp are listed as Schedule A of the AIS Regulation under the provincial Water Protection Act and the AIS regulations under federal Fisheries Act. Possessing any of these listed species in Manitoba is illegal.

To learn about Manitoba's aquatic invasive species legislation under The Water Protection Act, please visit the following links:

Unconsolidated amendments to The Water Protection Act (bill 12):

AIS Regulations:

To learn about the federal AIS regulation, please visit:

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