Sophie Kuijper Dickson, LJI Journalist
A biologist brought in by the Municipality of Otter Lake to assess the presence of Eurasian watermilfoil found the invasive aquatic plant in three of the six lakes surveyed this August.
The report produced by biologist Annie Parent, received by the municipality at the end of September, found that Clark Lake, Leslie Lake and Hughes Lake seem to be free of contamination, although the biologist states that this does not mean it isn’t growing there.
Parent did however find several places where milfoil was growing in McCuaig Lake, Little Hughes Lake, and Otter Lake. Its presence in these three lakes is in addition to Farm Lake and Little Cayamant Lake, where the invasive species was first discovered in 2023.
The rapid growth of milfoil on Farm Lake led the municipality to close the lake’s boat launch this summer, leaving it open for cottagers to get on and off the lake on weekends, and put buoys on the lake to mark the contaminated areas.
The freshwater plant, nicknamed the zombie plant because of how difficult it is to kill, is of concern to the municipality because it outcompetes native lake species, reducing biodiversity and leading to poor water quality.
It grows to the surface of the water during the spring and summer, and dies out in the winter, at which point its decomposition consumes oxygen in the water, a process which can be harmful to aquatic life.
“It would be so thick that it would make swimming completely difficult, like a mat,” said Jennifer Quaile, pro-mayor of Otter Lake, describing the damage the plant could cause.
Also, boating becomes a problem because it’s a fragile kind of plant and it will wrap around your propeller to the point where you’ll get stuck.”
Also this August, the municipality had a whole team of biologists conduct a more extensive mapping effort on Farm Lake and Little Cayamant Lake. The results of that work are expected in early November, according to Quaile, and will indicate not only where each growth is, but how much of it there is in each location.
This information will be used to determine which strategy the municipality should employ to get rid of the milfoil. The options, according to Quaile, are placing a tarp over the affected areas of the lake, or having divers remove the milfoil plants at their base.
“If you’ve got a patch of growth and there’s 80 per cent milfoil, they’re going to suggest we use the tarp, if it’s a large area with that much milfoil. And that will kill off the natural plant as well, but it’s worth it,” Quaile said. “Pulling it out by hand is recommended in smaller areas.”
Maps included in Parent’s report mark the locations on each lake where the milfoil was found, but the report states there may be more, as the survey done did not investigate every corner of each lake.
Quaile said she was surprised the plant hasn’t reached all lakes yet.
“And the biologist was surprised too because the conditions are quite favourable. Leslie lake is a shallow lake and the plant grows quite well when the sunlight can get to it. And again with Hughes, because there’s a creek that runs out of Farm into Hughes,” Qualie said. “So I think there’s a lot of factors that even the scientists aren’t sure of yet.”
While the mitigation work being done on Farm Lake is ahead of the other four lakes where the milfoil has been found to date, Quaile said council will work with a committee that includes representatives from each lake’s association to determine how best to proceed.
“Once we have our strategies figured out with the committee’s recommendations to council, we’ll go and get public feedback.”