In 2018, plant surveyors on Cobbosseecontee Lake found Eurasian Watermilfoil (Myriophyllum spicatum L. or EWM), a non-native plant originally from Europe and Asia. This plant can quickly spread throughout a body of water due to the absence of natural competitors. If not managed, an EWM infestation can have severe consequences, including the formation of dense mats that hinder boating, fishing, and swimming. Additionally, it can degrade water quality and reduce the value of shoreline properties.
To manage EWM in Cobbosseecontee, various control methods have been employed, including manual removal of the plants, benthic barriers, herbicide treatments, annual surveys, and Courtesy Boat Inspections conducted by trained staff and volunteers. Despite these efforts, as of 2023, EWM has also been detected in Cobbosseecontee Stream, however it was not found during surveys in 2024 or 2025. Due to the nature of the plant, EWM spreads easily via fragmentation, meaning small portions of the plant can be broken off and will re-root in a new location.
