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 Massachusettes. Populations were also 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. Sixteen other lakes or ponds in Vermont have now been confirmed with water chestnut: Brookside, Pond, Bullis Pond in Franklin Coggman Pond, Pelkey's Swamp, Parson's Mills Pond, Lake Paran, Lake Bomoseen, Porter Lake, North Springfield Reservoir, Richville Pond, Root Pond, a small private pond in Bennington, Singing Wetland in North Bennington, Lily Pond in Poultney and three small ponds in Benson. Annual surveillance and handpulling has kept water chestnut controlled in those waters. In 2010, water chestnut continued to be handpulled from several wetlands in Missisquoi Bay National Wildlife Refuge.
In Canada, water chestnut was first reported in Quebec in 1998 in the South River, a tributary to Lake Champlain's outlet, the Richelieu. Since 1998 the population of water chestnut has increased dramatically 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. During a survey in the summer of 2001, water chestnut was discovered in the Pike River which flows into Mississquoi 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.
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 2010.
Management
Mechanical harvesting and hand removal have been the main means of water chestnut management for the last 28 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 the lake water chestnut 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 lake in 1967. The control program was terminated in 1971 because water chestnut had mostly eliminated from southern Lake Champlain and there was no funding for the program. By 1982, the water chestnut population 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 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. Water chestnut has now re-infested all the areas where it had previously been controlled. The northernmost confirmed location in Vermont Lake Champlain waters other than in Missisquoi Refuge at the northern end of Lake Champlain is in Little Otter Creek in Ferrisburg, Vermont. Water chestnut has also been confirmed in fourteen 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 eight million dollars has been spent controlling water chestnut in both sides of Lake Champlain. New York State has contributed $788,260 (9%), compared to $2,992,875 (34%) spent by the State of Vermont, $1,241,544, (13%) spent by the Lake Champlain Basin Program, $214,596 (2%) spent by United States Fish and Wildlife Service (USFWS), and $3,648,736 (41%) by the Army Corps of Engineers through its Aquatic Plant Control Program. Ducks Unlimited contributed $10,000 to the water chestnut management effort in 2002 and another $5,000 in 2003.
Funds for water chestnut management in 2010 totaled $584,200 including a NY. New York State managed a mechanical harvesting program in the Town of Dresden north of Whitehall, NY for seven weeks in 2010. The VT Department of Environmental Conservation contributed $150,000, the Lake Champlain Basin Program contributed $75,000, New York contributed $75,000 the Army Corps of Engineers contributed $326,900, USF&W ANS gave $20,000 and US F&W Partners Program provided $10,000. Most available funds were expended and the Vermont control program ended for the year in the beginning of September. New York started harvesting in July in the South Bay area of Lake Champlain and ended at the beginning of September near Dresden Landing.
Vermont's commitment to funding water chestnut management is paying off. For the first time in 2010, the VTDEC contracted harvesters worked done to the Narrows of Dresden further south than they have ever gone before. All water chestnut sites north of Benson Landing were controlled by handpulling in 2010.
The Canadian water chestnut control efforts in the South River, a tributary of the Richelieu River located in Henryville, Quebec continued in 2010 although water levels were very low, twelve years after the discovery of water chestnut in Canada. All of the control work being done currently consists of handpulling. 2010 water chestnut sites 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. Also, management of the Ottawa River water chestnut population is planned again for 2011.
Additional Information
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Watershed Management Division 
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