Blue planet, green ideas | An unequal fight against the invader of the lakes

Biologists can tear it out, suffocate it, poison it, but it’s useless; Eurasian watermilfoil has become an irrepressible invader of lakes in Quebec. Described as a “zombie” plant, it is almost everywhere. Failing to be able to eradicate it, complex and costly interventions are still multiplying this summer, to at least control it.

This invasive plant (Myriophyllum spicatum) has taken root in 184 lakes and 22 rivers in the province, in 2023, according to the most recent survey by the Ministry of the Environment, the Fight against Climate Change, Wildlife and Parks (MELCCFP) transmitted to The Press. The most invaded regions are the resort lakes of Estrie, Laurentides and Outaouais. Almost all regions are affected, including Montreal, indicates the Ministry. Only the Gaspésie and Saguenay–Lac-Saint-Jean regions are exempt. But it’s only a matter of time, biologists say.

“Never the end”

With an area of ​​around twelve square kilometers, Lake Papineau, in the Outaouais, is one of the jewels of Quebec’s resort area. The lake is known for its crystal clear water and swimming. It is popular for navigation and lake trout fishing. But now the spawning grounds of this fish – the place where it lays its eggs – are apparently being swallowed by Eurasian milfoil.

The biologist and his team have manually pulled out 423 pounds of Eurasian milfoil from Lake Papineau since last year, putting them back on a boat in airtight bags. A 3,600 square meter tarpaulin, made from 25 canvases, was ballasted. The tarpaulin served to crush seven beds of invasive plants in this lake.

This procedure alone cost $120,000. It was financed by the riparian community, Boileau du lac sector, and benefited from a grant from the Nature Conservancy of Canada (CNC). According to studies carried out by MELCCFP experts, the cost of one hectare to treat can amount to $200,000. Several factors explain these costs, including the ability of the invasive plant to reproduce on its own, from a small fragment of stem.

“And it’s never the end,” specifies biologist Jérémie Isabelle, of the Rappel cooperative, who also carries out operations at the two clear water lakes, Stukely and Fraser, in Mont-Orford national park, a mandate awarded by the Société des establishments de plein air du Québec (SEPAQ).

“There is a maintenance struggle to be carried out every year, we must ensure the delicate uprooting of new seagrass beds. In certain lakes, we can hope to reach below the detection threshold. For example, we have had good results with small Lake O’Malley, near Orford, but we can never speak of total eradication. »

From one scientific journal to another, Eurasian watermilfoil is described as a plant with branched stems that can reach up to six meters. The invasive plant has a habit of erecting itself until it reaches the surface. Unsavory green, slimy, it should not be confused with algae or other plant species. Milfoil is found in lakes, but also in natural and artificial ponds, as well as in marshes, bays with calm waters of rivers and rivers.

Waters of ballast and legends

According to the Ministry of the Environment, the plant was probably introduced to North America through the ballast water of ships coming from Europe, Asia or Africa. Other hypotheses suggest that it was used as an aquarium plant, or transported by migratory birds. In Quebec, it has been present since at least 1958.

Claude Lavoie is professor and director of the Superior School of Land Planning and Regional Development at Laval University. He is a specialist in the ecology and management of invasive plants. In this capacity, he collaborated with the Ministry of the Environment to draft the reference document listing Eurasian watermilfoil in 184 lakes.

“There are all kinds of legends, each more eccentric than the last, surrounding Eurasian watermilfoil,” explains Claude Lavoie. For example, I hate the expression “zombie”. We decided to call it that because it naturally fragments to take root. But the plant has never eaten anyone, as far as I know. »

Mr. Lavoie studied six methods to combat milfoil, in addition to unproven interventions. Hypotheses. One of them consists of introducing a herbivorous insect, the weevil, but experiments carried out in Lac-Supérieur have been unsuccessful. Especially since the insect in question is prized by certain fish. Another would be to install an ultraviolet ray-emitting platform, but this is controversial due to its destructive environmental impact. There would indeed be the introduction of a grass carp, a voracious species of this plant, but it is considered invasive, and its introduction is “strictly prohibited” in Quebec.

“I believe that neighboring property owners must ask themselves questions about their level of tolerance. Perhaps they should limit themselves to cleaning swimming areas and ensure visual inspections of boats? Because there is little data demonstrating that Eurasian watermilfoil is harmful to ecosystems, to fish,” explains Mr. Lavoie.

In George and Upper Saranac Lakes, in New York State, a colossal grubbing operation was “a flamboyant success,” he adds. But this large-scale investment did not make it possible to completely eradicate the plant, recalls Mr. Lavoie, and the operation will have to be repeated in perpetuity.

Visit the website of the water protection solidarity cooperative, Reminder

Consult the guide Prevention and control of Eurasian milfoil 2023