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Zebra mussels

Zebra mussel next to a dime on a person’s hand.

Tiny zebra mussels are an aquatic invasive species.

Enlarge image: Zebra mussel next to a dime on a person’s hand.

Zebra mussels are an aquatic invasive species native to Europe. Zebra mussels were introduced to North America in the late 1980s through cargo shipping. They were first detected in Lake Erie. In a few years they had spread into the rest of the Great Lakes. Since then, zebra mussels have spread to Manitoba.

They were first detected in the Lake Winnipeg south basin in 2013 and have now spread downstream. In 2019, zebra mussel larvae (veligers) were found in the Nelson River up to the Limestone generating station near Gillam.

Without treatment, zebra mussels pose a significant risk to the safe operation of generating stations. Zebra mussels can grow inside pipes, reducing or blocking water flow to critical systems for unit cooling and fire protection. With the increasing spread of zebra mussels, we will need to begin treating for zebra mussels at facilities along the Nelson River.

Controlling zebra mussels within our facilities

Zebra mussel growth in critical generating station pipes can be controlled using a low-level chlorine treatment. Chlorine treatment is the most effective method to control adult zebra mussel growth and is widely used at other hydroelectric generating stations in North America.

When needed, treatment will be administered within generating station pipes once a year when water temperatures are above 15°C. The treatment will control zebra mussel growth in essential pipes. The concentration of chlorine used in the treatment is similar to levels found in municipal drinking water.

Treatment will be conducted by an experienced contractor for approximately 2 weeks per facility. The chlorinated water will be de-chlorinated before it leaves the station. Monitoring will take place over the course of the treatment to ensure the water is de-chlorinated before it is discharged.

Treatment schedule

Updated October 2021: In 2021, low-level chlorine treatment occurred at the Jenpeg, Kelsey, Kettle, Long Spruce, and Limestone generating stations. Future treatment plans will be determined in spring 2022.

Manitoba Hydro chlorine treatment process.

View a cross section of a typical generating station showing the chlorine treatment and monitoring process.

Enlarge image: Manitoba Hydro chlorine treatment process.

Treatment and aquatic life

No effect on fish or aquatic life is anticipated. The zebra mussel treatment will target pipes within the generating stations, and this water will be de-chlorinated before it is discharged from the station. Monitoring will take place over the course of the treatment to ensure the treatment solution is de-chlorinated before it is discharged. Manitoba Hydro’s zebra mussel treatment plan was developed with the help of industry experts and has been approved by the Pest Management Regulatory Agency of Health Canada, Manitoba Conservation and Climate, and Manitoba Agriculture and Resource Development.

COVID-19 safety

To protect all communities, Manitoba Hydro employees and contractors, Manitoba Hydro must develop a plan and adopt safety protocols recommended by Manitoba Health, including testing and mandatory isolation after travel internationally and inter-provincially. Additionally, contractors and Manitoba Hydro staff must direct all staff to not come to work if they exhibit cold or flu symptoms, and to screen their return to work through a health professional.

More information about zebra mussels can be found on the Province of Manitoba’s Stop Aquatic Invasive Species website.