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.”
