Courtesy of www.invasivespeciescentre.ca
Eurasian watermilfoil
Invasive aquatic species on the rise in Quebec
By William Crooks
Local Journalism Initiative
With boating season underway across Quebec, scientists and environmental groups are sounding the alarm about a growing threat to the province’s waterways: invasive aquatic plant species. Among the most concerning are Eurasian watermilfoil and water chestnut, which are spreading rapidly across southern Quebec and disrupting ecosystems in lakes and rivers.
Dr. Morgan Botrel, a postdoctoral researcher in aquatic plant ecology at McGill University, explained in an interview with The Record that these species not only outcompete native plants, but also harm water quality and biodiversity. “Eurasian watermilfoil spreads easily because it reproduces from fragments,” she said. “Once it gets into a lake, it forms massive beds that block sunlight and reduce oxygen, which impacts fish and other fauna.”
Botrel’s background includes a PhD on aquatic vegetation in Lac Saint-Pierre, where she found that native plant beds can actually filter pollutants and help regulate carbon cycles. “We need to talk more about the benefits of native aquatic plants,” she said. “They provide essential ecosystem services, and it’s important that people don’t confuse them with invasive species and start pulling them out.”
While Eurasian watermilfoil has long been a concern in the Eastern Townships and the Outaouais, water chestnut is an emerging problem in the Saint-François and Yamaska rivers. Native to Europe and Asia, the floating plant produces hard chestnut-like seeds and forms dense surface mats. “Once the chestnuts fall and take root, it’s very difficult to get rid of them,” said Botrel. “They block light and oxygen, and mechanical removal is labour-intensive.”
Botrel emphasized that early intervention is key. “Diving teams can be effective in small areas, but it’s time-consuming. The most strategic approach is prevention—identifying vulnerable lakes and using early detection tools like environmental DNA sampling.”
In 2024, the Regional Environmental Council of Estrie (CREE) confirmed the presence of the Georgian viviparid, a new invasive snail species, in Brompton Lake. During a packed press conference in Saint-Denis-de-Brompton, Dr. David O’Connor of the CREE explained that the species is hard to detect due to its planktonic larvae, and urged proper boat and equipment decontamination using hot, high-pressure water. “Even a small amount of water in a life jacket or some soil on water shoes can transport these species,” he warned.
CREE has since classified lakes in Estrie by their risk level: “Red” for those harbouring hard-to-detect invasive species, such as zebra mussels or viviparids, and “Yellow” for more manageable threats like watermilfoil. Brompton Lake, Memphrémagog, and the Magog River are among the red-level sites, requiring stringent cleaning protocols before and after use.
A second 2024 report, focused on Lake Memphremagog, highlighted the international dimensions of the problem. The Memphremagog Watershed Association (MWA) in Vermont and its Canadian counterpart, Memphremagog Conservation Inc., continue to coordinate efforts to stop the northward spread of zebra mussels and other invasive species across the Canada–U.S. border. “We’re seeing zebra mussels move from Magog toward Georgeville,” MWA’s Jennifer Hopkins noted, citing the lake’s northward flow and the role of wake boats in spreading larvae.
Efforts on both sides of the border include “Clean, Drain, Dry” campaigns, boat inspection stations, and public awareness initiatives. However, as Hopkins pointed out, “There’s no single body formally coordinating everything,” underlining the ongoing need for cross-border regulatory alignment.
Botrel agreed that more could be done. “We need better integration of local knowledge,” she said, explaining that much of Quebec’s plant data is scattered across different sources, including the Organismes de bassins versants (OBVs)—non-profit watershed management organizations that monitor water quality and coordinate environmental action in specific drainage basins. Her current work involves compiling this fragmented data to better understand how native plant communities might resist invasion. “We may find that degraded lakes are more vulnerable,” she said.
While new technologies like AI-guided amphibious drones and environmental DNA detection are promising, Botrel stressed the importance of consistent action from the public. “Washing boats properly isn’t just about stopping the spread,” she said. “It’s about protecting the future of our lakes.”
As Botrel and others continue their work in May 2025, one message rings clear: aquatic ecosystems in Quebec are under pressure, and everyone has a role to play in safeguarding them.