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Zebra mussels in Manitoba’s waterways are a cause for concern

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In Manitoba, it is illegal to transport zebra mussel contaminated water equipment, such as boats, trailers and float planes, from one water body to another.

By Damodar Pokhrel

The zebra mussel, an aquatic invasive species native to the Black and Caspian Seas in southeastern Europe, was first discovered in a harbour in Lake Winnipeg South Basin in 2013. Since then, they have been found in Lake Winnipeg North Basin and other lakes in Manitoba, including Emerson Lake, Cedar Lake and Singush Lake in Duck Mountain Provincial Park.

Generally found in a fresh/marine water environment, at a depth of 4 m – 7 m and a salinity of 1.75 – 3.5 ppt., zebra mussels inhabit and reproduce well in an oxic environment with oxygen levels from 0.1 – 11.2 mg/L and temperatures at 20°C – 25°C. In ideal environmental conditions, the female mussel can produce as many as one million eggs in a single spawning season.

The fertilized egg develops into veliger in 3 – 5 days and becomes a free-swimming larva in about a month’s time. The reproductive rate of zebra mussels drastically decreases at temperatures below 10°C. They generally live 6 – 9 years and can survive out of water for up to 30 days, depending on temperature and humidity.

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The impact of the zebra mussel invasion in Lake Winnipeg and other lakes in Manitoba is relatively new and is yet to be understood. Based on the literature and available information from other areas in Canada and elsewhere, the potential impacts include changes to the ecological environment, negative effects on the local economy, and severe fouling of water infrastructure.

Ecological environmental impacts could include changes in lake water quality, decrease in algae and diatom biomasses, and zooplankton populations, resulting in a severely unbalanced food chain. Adult mussels compete with large zooplankton for food which affects the food flux of the impacted lake, ecosystem and structure of the aquatic environment. Small fish that thrive on algae and zooplankton may not have enough food. Larger fish that depend on the small fish could starve, which may lead to extinction.

The ecological impact of the zebra mussel invasion in Lake Erie has been documented by Holland, R.E. (1993). According to this study, the algae population of Lake Erie decreased by 90% and diatom biomass declined 82% – 91% after the invasion. Transparency of the lake increased by 100% within a year due to a decrease in algae biomass. Zebra mussels depend on algae for food and filter approximately one litre of water in a day.

On a positive note, zebra mussel invasion reduces cynobacteria and blue green algae populations, which in turn decreases eutrophication. According to a 2015 Global News report, the cost of controlling zebra mussels in water intake pipes in the Great Lakes is $250 million annually.

History in Manitoba

Zebra mussels were introduced to Laurentian Great Lakes in the mid 1980s as a result of ballast water discharge from ships. Subsequently, the species was either transported or migrated to the western United States and Canadian provinces. According to a US Geological Survey, this species was first discovered in Red Lakes, Minnesota in 2010. Red Lake River originates at Red Lakes and joins the Red River at Grand Forks, North Dakota.

The Red River enters Canada at Emerson, and flows through the city of Winnipeg to Lake Winnipeg. It is suspected that zebra mussels migrated to Lake Winnipeg via the Red River. Subsequent to their discovery and confirmation in Lake Winnipeg in 2014, the province followed with intensive monitoring at Emerson and in certain locations of the Red River.

The results were negative, but adult zebra mussels were found in floating debris in Lake Winnipeg. In 2015, veligers were found in the Lake Winnipeg Channel, as well as in the Lake Winnipeg North Basin. Adults were found in both the Red River near Emerson and in Cedar Lake. In 2017, two other suspected infested water bodies were identified.

After the first discovery of zebra mussels in Lake Winnipeg, the Canada-Manitoba Fishery Advisory Committee (CMFAC) was formed to develop a rapid response plan and to advise the province on how to eradicate zebra mussels from four harbours, and to control their spread.

The task group was composed of specialists from the Department of Fisheries and Oceans and the Government of Manitoba Aquatic Invasive Species Branch. The government also formed the Manitoba Zebra Mussel Science Advisory Committee.

In 2014, the CMFAC developed early detection rapid response plans to eradicate zebra mussels from the impacted harbours. Options considered by CMFAC were to do nothing or try physical, chemical and biological treatment. Chemical treatment was considered to be the most effective. Options evaluated were pH reduction, injecting copper sulfate, chlorine or liquid potash.

The pH reduction option was rejected, as this method had not been tested elsewhere. In addition, maintaining low pH was technically challenging and there was uncertainty as to its effectiveness because zebra mussels have been reported to survive even at pH 5.2.

Copper sulfate has been used to eradicate zebra mussels elsewhere but was not a registered product with the Pest Management Regulatory Agency (PMRA), which regulates pesticides in Canada. Furthermore, it is toxic to fish and other aquatic life and could be detrimental to the life of non-target species.

Chlorine has been utilized the most to mitigate zebra mussels, but required regulatory approval for use in Manitoba. It is also toxic to fish and non-target species and so was rejected.

Liquid potash had been successfully used in the United States to eliminate zebra mussels from a quarry in Virginia and has low health risks from exposure for humans and non-target species. Even though it was not a registered product, PMRA authorized this product for research purposes. In May 2014, the province closed Arnes, Gimli, Winnipeg Beach and Balsam Bay harbours where zebra mussels had been found. Liquid potash was used to eliminate the mussels before the temperature rose to 12°C. The province had some success, but veligers were detected in Lake Winnipeg South Basin and the Red River.


Anthropogenic activities, especially fishing and recreational boating, kayaking, float planes, overland transporting of canoe and water equipment, have been reported as vehicles for the transport of zebra mussels in Canadian fresh waters (Darbyson et. al., 2009). Manitoba Fishery Regulations, which came into effect in 1987, prohibited import of zebra mussels into Manitoba. As of 1999, possessing and releasing them into the environment had been illegal.

The exercise to eliminate zebra mussels from Lake Winnipeg failed due to various reasons, including the large volume of water, high reproductive rate, and difficulty of controlling veliger transport via water conveyance. Subsequently, the province has adopted the strategy of regular monitoring, containing the species within the impacted lake, and preventing their transport to uninvaded lakes.

In November 2015, the government passed legislation to this effect and it is now illegal to transport zebra mussels from one water body to another. It is also illegal to transport zebra mussel contaminated water equipment, such as boats, trailers and float planes, from one water body to another.

Owners of water equipment require authorization before transferring the equipment and it must be cleaned, drained, dried and decontaminated. This involves high pressure washing with hot water which kills the mussels. The government has also developed watercraft inspection programs and has established six inspection and control stations across the province. Under the regulations, the public has the obligation to report sighting of zebra mussels to the Manitoba Aquatic Invasive Species Branch, which has established hotlines to facilitate reporting of mussel sightings. As of October 2018, regulating officers can ticket anyone defying the regulations.

The regulations and other details can be found under Water Protection Act for the Province of Manitoba and under Fisheries Act for the Federal Government.


Zebra mussels in Lake Winnipeg and other lakes in Manitoba have a good potential to foul and/or plug infrastructure. They have hair-like filaments, called bysal-threads, by which they stick to hard surfaces. Colonies may have as many as one million mussels per square metre.

Communities that live around Lake Winnipeg and other lakes in the province, use them for water supply, irrigation, hydropower, fishing and recreational purposes. Owners and operators of drinking water systems and other infrastructure had been waiting for regulatory approvals to use chlorine to protect their infrastructure, as chlorine has been successfully used to control zebra mussels in other areas in Canada.

Ontario was grandfathered in to use chlorine in 1992. However, this was not the case in Manitoba and other provinces. The Pest Management and Regulatory Agency (PMRA) is currently exploring regulatory options for the use of chlorine to control zebra mussels. However, no time frame for the decision has been set. In the interim, PMRA reviews applications for chlorine use to mitigate zebra mussels on a case-by-case basis.

In September 2018, PMRA authorized the Office of Drinking Water to use chlorine to mitigate zebra mussels at potable water intakes in Manitoba under certain guidelines. The major technical requirements for the use of chlorine are that chlorine shall be in the form of sodium hypochlorite, and that it be injected at the intake and then conveyed to the water treatment plant. Also, free residual chlorine concentration at the intake shall not exceed 5 ppm when water temperature exceeds 12°C.

Utilities opting to add a chlorine injection system to their intakes that comply with these guidelines need to get approval from the Office of Drinking Water. Utilities that intend to use chlorine, but do not meet these guidelines, need authorization from PMRA before making an application to the Office of Drinking Water.

Damodar Pokhrel, PhD, P. Eng, is with Infrastructure and Housing, Indigenous Services Canada and is based in Winnipeg. This article appears in ES&E magazine’s June 2019 issue.

(References are available upon request.)

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