While working on a unit at Jenpeg Generating Station last fall, one of our station staff felt a crunch under every step similar to walking on gravel. The crunching came from zebra mussel shells, the aquatic invasive species that as of 2020 has been discovered in all of our Nelson River generating stations.
Zebra mussels were introduced to North America in the late 1980s through cargo shipping and first detected in the Great Lakes. In 2013 they were detected in Lake Winnipeg, and by 2019 the Nelson River. Since then, the invasive species’ population has rapidly increased.
“In places like Stephens Lake, we’ve seen populations grow by 100,000% in 2020 alone,” said Mathew Bannerman, an environmental specialist at Manitoba Hydro.
Manitoba Hydro has taken a leading role in tracking and monitoring zebra mussels in Manitoba’s river system because it poses a risk to the safe operation of our generating stations. If not treated, zebra mussels can grow inside pipes, reducing or blocking water flow to critical systems for unit cooling and fire protection.
How are we controlling zebra mussels inside our stations?
We are planning to use a low-level chlorine treatment in the summer of 2021. 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.
“We’re using residual amounts of chlorine – 0.6 ppm – similar to the concentration of chlorine you’d find in your drinking water,” said Mathew. “Once the chlorine has passed through our raw water lines, we then neutralize it before being released to the Nelson River.”
When needed, treatment will be administered within generating station pipes once a year.
How do we track zebra mussels?
We have bio-boxes set up at our northern generating stations that track zebra mussel growth in our systems. A bio-box is a live look into the raw water that’s flowing through the station.
Zebra mussels attach to the plates in the bio-boxes and our chemists scrape the mussels off the plates to get a density count. This allows us to gain an understanding of how many mussels are growing within each station and better prepare for when chlorine treatment of our systems is required.
During the pandemic travel has been severely limited, which called for some extra cooperation between departments.
“It’s really been a joint-effort,” said Mathew. “Environmental staff haven’t been able to travel to site for monitoring and visual inspections as often because of the pandemic, so we’ve leaned on operations and maintenance to take a leadership role.”
Manitoba Hydro staff who work near or on waterways have online training available to help them understand the rules and guidelines of waterways that are impacted by zebra mussels.