In 2015, ABV7 (l’Agence de bassin versant des 7) conducted the initial assessment of Eurasian watermilfoil (Myriophyllum spicatum) in the Cedar lakes, revealing a significant presence in Petit lac des Cèdres while notably absent in Grand Lac des Cèdres. 

Subsequent detection inventories were undertaken in August 2018 and 2019, employing the methodology endorsed by the Réseau de surveillance volontaire des lacs (RSVL) of the ministère de l’Environnement et de la Lutte contre les changements climatiques (MELCC). Volunteers received comprehensive training in aquatic invasive species, plant identification, inventory techniques and specimen handling. Across multiple days in 2018 and 2019, these efforts revealed the presence of Eurasian watermilfoil in seven distinct weedbeds in Petit lac des Cèdres, covering a total area of 1.2 hectares or 12,000 square metres (specimens verified by the RSVL).

In contrast, Grand lac des Cèdres showed no sign of Eurasian watermilfoil. Instead, the surveys identified various native milfoil weedbeds, primarily Myriophyllum sibiricum, along with other non-invasive species.