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 47 miles between Whitehall,
New York and Ferrisburg, Vermont (view map). Eight Lake
Champlain tributaries, including two in Canada, support water chestnut populations. Eleven other lakes or ponds in Vermont have now been confirmed
with water chestnut: Coggman Pond, Pelkey's Swamp,
Parson's Mills Pond, Lake Paran, Lake Bomoseen, Porter Lake, North Springfield Reservoir, a small private pond in Bennington and one in North Bennington, Lily Pond in Poultney and a small pond in Benson. Annual surveillance
and handpulling has kept water chestnut contolled in those waters. In 2006, water chestnut
was found and 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.
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 2006.
Management
In southern Lake Champlain, water chestnut currently invades a range of 47 miles, extending from Whitehall, New York in the south north to Ferrisburg, Vermont, and as of 2005 and 2006 is invading from the north also in wetland and river areas in Missisquoi Wildlife Refuge. In Vermont, mechanical harvesting and hand removal have been the main means of water chestnut management. 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 been supposedly 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 reinfested 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, almost seven million dollars has been spent controlling water chestnut in both sides of Lake Champlain. New York State has only contributed $569,958 (8%), compared to $2,339,496 (35%) spent by the State of Vermont, $925,544, (14%) spent by the Lake Champlain Basin Program, $141,170 (2%) spent by United States Fish and Wildlife Service (USFWS), and $2,738,048 (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 2006 totaled $466,000 including NY. New York State managed a harvesting program in the Town of Dresden north of Whitehall, NY for three weeks in 2006. The VT Department of Environmental Conservation contributed $150,000, the Lake Champlain Basin Program contributed $63,000, and the Army Corps of Engineers contributed $200,045, several US F&W sources provided $20,481, and USDA Whip contributed $7,650. All available funds were expended and the Vermont control program ended for the year on August 25. New York started harvesting in July in the Dresden area Lake Champlain and ended in mid August. No Army Corps of Engineers funds were available to Vermont for water chestnut management in 1997 and 1999 but since 2000 the Corp's Aquatic Plant Control Program budget has been funded at approximately the same level.
Vermont's commitment to funding water chestnut management is paying off. In 2006, the northern most mechanical harvesting site is approximately one mile south of Benson Landing, VT. All water chestnut sites north of Benson Landing were controlled by handpulling in 2006.
The Canadian water chestnut control efforts in the South River, a tributary of the Richelieu River located in Henryville, Quebec continued in 2006, eight years after the discovery of water chestnut in Canada. Most of the control work currently consists of handpulling. Additionally several small boats equipped with a Biocaptor device is being used in the South River. handpulling work in being done in the Richelieu River and in the John Pond wetland area near Venise en Quebec at the northern end of Missisquoi Bay.
Additional Information
Updated: November 2004
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Water Quality Division 
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