Combating Invasive European Water Chestnut
European Water Chestnut (Trapa Natans) is an invasive aquatic plant, originally brought to the United States in the late 19th century. This plant has spread rapidly along the East Coast, outcompeting native plants for space and nutrients, and now threatens the health of many of CT’s rivers and lakes. It was first identified in the Pomperaug River Watershed at Lake Stibbs (Southbury Training School Pond) in 2016 by field staff of CT DEEP's Inland Fisheries Division. PRWC has been working to control its spread in Lake Stibbs and downstream in the Pomperaug River and Lake Zoar since 2020 to protect clean water, healthy habitats, and safe recreation for all of our watershed residents.
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version of this interactive map.
As with any invasive species, the most effective management tactic for water chestnut is prevention. Regularly monitoring for new growth and removing plants and seeds as soon as they are found is an essential part of our water chestnut management efforts.
The map above shows water chestnut sightings documented by our staff and volunteers during stream walks and paddle surveys from 2023–2026. When water chestnut is found, plants and seeds are carefully removed and properly disposed of onshore to help prevent further spread. Once a sighting is documented, staff will continue to monitor the area in following seasons to catch any regrowth and determine whether more extensive management efforts are needed.
Recent Management Success
In 2026, PRWC volunteers and staff were successful in manually removing over 509 bushels (approx. 12,725 lbs) of European water chestnut plants from Lake Stibbs and the downstream systems of Transylvania Brook, Pomperaug River, and Lake Zoar through water chestnut pulls, paddle surveys, and streamwalks.
PRWC plans to continue its work to protect the Pomperaug River by restoring the health and recreational function of Lake Stibbs and preventing invasive water chestnut from impacting habitats and recreation areas downstream in the Pomperaug River and Lake Zoar.
Further downstream spread of invasive European water chestnut would be detrimental to important cold-water habitats and to the boating, fishing, and swimming opportunities provided in Lake Zoar. Removing this invasive plant therefore benefits residents by improving and protecting habitat and water quality for the rainbow, brown, and wild brook trout that provides some of the best freshwater sport fishing in the region, while also extending environmental education, youth development, and service opportunities.
Want to Get Involved?
We need ongoing support from our community members to help identify and manage invasive European water chestnut in the Pomperaug River Watershed. Based on the growth cycle of water chestnut plants, we host our tracking and removal programs between June and August each year. If you are interested in participating in future invasive water chestnut tracking and removal efforts with PRWC, please let us know!
Seen This Plant?
If you spot invasive water chestnut in lakes, rivers, or streams within the Pomperaug River Watershed, please report it to PRWC by filling out our public water chestnut observation form.
