Inventory of Eurasian watermilfoil weedbeds

Eurasian watermilfoil (Myriophyllum spicatum) is an exotic invasive aquatic plant found in many lakes in Quebec, including Lake Memphremagog and its watershed. It can grow in very dense weedbeds, impacting the attractiveness of bathing areas and harming the development of native species and navigation. Its stalk resembles long coils and its leaves are finely cut, like feathers. A fragment of Eurasian watermilfoil (cut, for example, by a boat propeller) can easily drift with the current and create a new weedbed. To report a Eurasian watermilfoil sighting, visit

Operation Healthy Lake

Operation Healthy Lake is a project initiated by MCI in 2004 in Lake Memphremagog. Its main objective was to assess the state of health of the body of water. The activities carried out included an assessment of the invasion by aquatic plants, including the Eurasian watermilfoil. This study made it possible to establish the basis of our knowledge on the invasion of Eurasian watermilfoil in Lake Memphremagog by carrying out transects along the shores and by evaluating the density of weedbeds. Two studies were produced, one in 2005 (Canadian side) and one in 2006 (American side).

2020 inventories

In 2020, the MCI patrol accompanied a bioecology technician student in his inventory of watermilfoil weedbeds in Lake Memphremagog. A total of 21 weedbeds had been identified. An internal report was also produced.

2022 inventories

During the summer of 2022, MCI's team carried out a large-scale project to survey the Eurasian watermilfoil weedbeds. In total, 108 weedbeds containing watermilfoil have been identified, over approximately 30 km of shoreline. 23 maps were also produced during this study (see bottom of page).


Portrait of Eurasian watermilfoil in Cummins Bay. More than a hundred weedbeds were delimited and characterized by MCI in 2022.

Inventory of Eurasian watermilfoil in Lake Memphremagog (French only)

MCI study carried out in 2022. Report written by Roxanne Tremblay, MCI project manager.