Water chestnut, an annual emersed plant native to Eurasia, was introduced to North America in the latter part of the nineteenth century and is now known to infest waterbodies in Massachusetts, Vermont, New York, Maryland, Virginia and most recently the Connecticut River in Connecticut. Its origin in the US stems from its introduction into a water garden in Fresh Pond, Cambridge, Massachusetts, in the 1870’s, by a gardener who planted it in several other aquatic locations as well. Between 1982 and 2000, the states of New York and Vermont invested over $3.6 million to control its growth in Lake Champlaine.

Photo - Right: Trapa Natans or Water Chestnut fruit - From the Invasive Plant Atlas of New England, University of Connecticut Library.

It’s a rooted, floating plant that can grow in 12 to 15 feet of water. It produces rosettes of strongly toothed, triangular leaves which cover the water’s surface, sometimes in layers 3 deep. In mid-summer, its small, four-petaled white flowers give way to the plant’s fruit -- a woody or bony nut, about 3 centimeters wide, with stout ½ inch spines capable of inflicting painful wounds if stepped on. Fruits may remain viable in bottom sediments for up to 12 years. Trapa natans is commonly found in placid, nutrient rich lakes and rivers with a pH of 6.7-8.2. Plants have also been found in freshwater regions of estuaries and exposed mud flats.

Photo - Left: Harry Waters, Swimming Beach and Boat Launch Attendant and Courtesy Boat Inspector at Kanokolus Boat Launch, Unity, Maine, displays the Water Chestnut fruit found on a boat trailer June 17, 2005.

It has frequently been said that waterfowl may transport water chestnut fruits over long distances, and a glance at the curved barbs would seem to bear this out. However, the fruits weigh about 6 grams and drop to the bottom of lakes “like sinkers”, making them unlikely hitch hikers for birds. On the other hand, the fruit’s empty shell is light and its transport may have led to the belief that waterfowl are a significant means of plant spread.

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Sources: Invasive Plant Atlas of New England; University of Connecticut Library; South Carolina Department of Natural Resources; US Department of Agriculture.