Water Chestnut

September 2025 – Jug Stream, Monmouth, Maine — In a significant development, a new aquatic invasive plant species has been identified in the Cobbossee Watershed. The diligent efforts of Cobbossee Lake Association (CLA) plant survey volunteer, Cheryl Soucy, have led to the discovery of a suspicious floating leaf plant. Prompted by this finding, Watershed Friends’ surveyors, along with the Maine Department of Environmental Protection (DEP) and CLA staff and volunteers, conducted a swift follow-up survey and confirmed the presence of Trapa natans, commonly known as Water Chestnut, in Jug Stream, south of the dam. Three plants were found and subsequently removed by the Watershed Friends’ Plant Control Coordinator, Em Russell.

Water Chestnut has the potential to spread rapidly as its barbed fruit can readily attach to boating gear and wildlife. The fruits dangle beneath the rosette of floating leaves, which commonly detach and float to new areas. Each seed can produce 15 to 20 new rosettes, and each rosette can generate up to 20 seeds. At the end of the growing season, the fruits fall and sink into the sediment, where they can remain viable for up to 12 years, though most germinate and form new plants within 2 years. Water Chestnut infestations can produce large, thick mats that can impact water quality and impede boating and recreation. This invasive species has not been documented in any other waterbodies in Maine.

This discovery highlights the importance of volunteer survey efforts and the impact of plant identification and other educational workshops. Soucy began volunteering as a CLA plant surveyor in 2022 and became Tier 2 IPP-Certified after attending a Lake Stewards of Maine (LSM) Live Plant ID Workshop in July 2025. Soucy has also attended a number of educational and plant identification workshops hosted by Watershed Friends. For more information regarding past LSM workshops and current educational opportunities, please visit their website: https://www.lakestewardsofmaine.org/ais-workshops/

Volunteer survey efforts have allowed Watershed Friends’ paid survey and control crews to respond to infestations more rapidly and have been integral in assisting with both early detection and rapid response surveys across the state. Volunteers can become involved with survey efforts within the Cobbossee Watershed via the “See it. Snap it. Send it.” program and/or the Adopt-a-Shoreline program.