Water Chestnut
Identification
Water chestnut, scientific name (Trapa natans L.), is an annual aquatic plant, with both surfacing and submersed leaves. Surfacing leaves are
triangular with toothed edges and an inflated petiole, or leaf stalk, and form a rosette on the water surface. Submersed leaves are feather-like; each leaf
is divided into segments that are whorled around the leaf stem. White flowers form in the axils of the surfacing leaves in July. Fruit are nut-like and
"woody" with typically four sharp, barbed spines. Long cord-like rarely branching stems can attain lengths of up to 16 feet. Water chestnut grows in freshwater
lakes and ponds and slow moving streams and rivers. It prefers calm, shallow, nutrient-rich waters. Click here
for a detailed image of water chestnut.
Reproduction
A true annual, water chestnut reproduces by overwintering seeds. Single-seeded woody fruits produced from pollinated flowers the previous year germinate in early spring. A single seed may give rise to 10 to15 plant rosettes. Each rosette can produce up to 15 to 20 seeds. Ungerminated seeds may remain viable for up to 12 years. However, most seeds probably germinate in the first two years.
Distribution
A native of Europe, Asia and tropical Africa, water chestnut was introduced to New York State in the late 1800s. From New York, water chestnut spread via interconnected waterways into Vermont and Massachusetts. Populations have also been confirmed but controlled in Virginia and Maryland. Water chestnut has recently rebounded in Maryland and now also has been confirmed in Connecticut, New Hampshire and New Jersey (view map).
In Vermont, water chestnut occupies significant areas of southern Lake Champlain and currently extends over a range of 91 miles between Whitehall, New York and Franklin, Vermont (view map). Nine Lake Champlain tributaries, including two in Canada, support water chestnut populations. Nineteen other lakes or ponds in Vermont have now been confirmed with water chestnut: Brookside Pond in Orwell, Bullis Pond in Franklin, Coggman Pond in West Haven, Pelkey's Swamp, Parson's Mills Pond, Horton Pond, Phillips Pond, Root Pond, and a small unnamed pond in Benson, Lake Paran, Singing Wetland and a small pond in Bennington, Lake Bomoseen in Castleton, Porter Lake in Ferrisburg, North Springfield Reservoir in North Springfield, Richville Pond in Orwell, and Lily Pond, and Little Lake in Poultney. Annual surveillance and handpulling has kept water chestnut controlled in those waters. In 2012, water chestnut continued to be handpulled from several wetlands in Missisquoi Bay National Wildlife Refuge as well.
In Canada, water chestnut was first reported in Quebec in 1998 in the South River, a tributary to Lake Champlain's outlet, the Richelieu River. Volunteer handpulling occurred in those early years with Vermont Department of Conservation (VTDEC) Staff spending much time north of the border handpulling water chestnut in the South River and adjacent areas. Since 1998 the population of water chestnut has increased dramatically in the South River and approximately 6 to 8 miles of the river from the mouth of the Richelieu River east to Henryville, Quebec is infested. There are also significant populations in the Richelieu River. During a survey in the summer of 2001, water chestnut was discovered in the Pike River which flows into Missisquoi Bay. Water chestnut was discovered in the mouth of the Missisquoi River in 2005, and in 2006 numerous plants were found in two large wetlands in Missisquoi Wildlife Refuge and in a tributary to Missisquoi Bay. In 2007, water chestnut was discovered in Ontario, west of Montreal in the Ottawa River near Point Fortune. The Quebec Ministry of the Environment has spearheaded water chestnut management in Quebec since 2001.
Work is currently conducted by contract and includes seven students and a supervisor. The contract is secured through 2015. Water chestnut populations occur in the South and Pike (Brochette) Rivers in Quebec; other areas of concern include the Richelieu River, Deux Montagnes Lake near Montreal, the Chateaguay River and the John Pond wetland area near Venise en Quebec at the northern end of Missisquoi Bay.
In 2011, surveying and non-mechanical harvesting work was conducted between July 4th and August 19th. Only 19,000 rosettes were pulled in 2011; at the start of the Quebec management program in 2001, 6.7 million rosettes were removed. No water chestnut was found in Missisquoi Bay, and only a few plants were found in the South River in 2011.
One new population of water chestnut was discovered in Quebec in 2011 in the Pike River, all plants found were removed. However of concern to Quebec is a relatively new population in Ontario. Future plans are to remove the water chestnut from Ontario and conduct surveys to prevent new infestations from becoming established and spreading into Quebec
Problem
Water chestnut is a fierce competitor in shallow waters with soft, muddy bottoms. Uncontrolled, it creates nearly impenetrable mats across wide areas of water. In South Lake Champlain, many previously often fished bays are now inaccessible and floating mats of chestnut can create a hazard for boaters. This noxious plant also severly limits the passage of light into the water, a critical element of a well-functioning aquatic ecosystem, reduces oxygen levels which may increase the potential for fish kills, out competes native vegetation and is of little value to wildfowl.
Control of Water Chestnut is Expensive!
Considerable taxpayer dollars are expended annually to control water chestnut in Lake Champlain and other Vermont waters. However leaving the problem untreated would result in losses to shoreline property values and decreases in recreational income from the lake. Funds for water chestnut management are appropriated from Federal and State sources. This pie chart indicates the amount of funding expended on water chestnut control in Vermont and Lake Champlain in 2011
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Management
Mechanical harvesting and hand removal have been the main means of water chestnut management for the last 31 years. Long experience has shown that these methods can be successful at controlling and reducing the infestation if infested sites are targeted repeatedly for five or more years. Since water chestnut overwinters entirely by seeds that may remain viable for years, repeated control is critical to deplete seeds in the sediment.
Twice in the history of water chestnut management in Lake Champlain the plant has been controlled. A control program instituted in Lake Champlain the '50s proved successful, resulting in only eight bushels of water chestnut being handpulled from the South Lake in 1967. The control program was terminated in 1971 because water chestnut had mostly been eliminated from southern Lake Champlain and there was no funding for the program. By 1982, the water chestnut population had rebounded. An estimated 300 acres of water chestnut existed over a range of approximately 20 miles of southern Lake Champlain. In 1982, the VT Department of Environmental Conservation, with funding from the Army Corps of Engineers, reinstituted a water chestnut management program for both sides of Lake Champlain. During the first nine years of the program, adequate funds were available and significant headway was made in reducing the size of the invasion. From 1991-1996, State of Vermont matching funds for water chestnut management were severely reduced, and the significant headway made in Lake Champlain the 1980s was entirely lost. The northernmost confirmed location in Vermont Lake Champlain waters other than Missisquoi Refuge and Bullis Pond at the northern end of Lake Champlain is in Little Otter Creek in Ferrisburg, Vermont. Water chestnut has also been confirmed in nineteen other lakes/ponds in Vermont.
Water chestnut is a bi-state and international problem in Lake Champlain. The states of New York and Vermont have not been equally sharing the burden of its control. Since 1982, more than 10 million dollars has been spent controlling water chestnut in both sides of Lake Champlain. New York State has contributed approximately 9% of the funds for the management effort compared to 34% spent by the State of Vermont, 13% spent by the Lake Champlain Basin Program, 2% spent by United States Fish and Wildlife Service (USFWS), and 41% by the US Army Corps of Engineers through its Aquatic Plant Control Program.
Funds for water chestnut management in 2012 totaled approximately $535,000 including the New York management program. New York State managed a mechanical harvesting program in South Bay, north of Whitehall in 2012, while Vermont DEC managed the program in the most of the rest of Vermont and on the New York side of the lake north of Ottenburg Landing. The Missisquoi Bay water chestnut populations were managed by US Fish & Wildlife staff in 2012 with help from VTDEC staff.
Vermont's commitment to funding water chestnut management is paying off. For only the second time since 1982, the VTDEC contracted harvesters worked south of the Narrows of Dresden. All water chestnut sites north of Benson Landing were controlled by handpulling in 2012.
Additional Information
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Watershed Management Division 
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