Chesapeake Bay Introduced Species Database

Trapa natans

Common name(s):
Water Chestnut
Trapa natans (Water Chestnut) was a widespread Eurasian water plant with edible seeds, and was introduced to North America as an ornamental plant in the 19th century. In the 20th century, it formed great blooms, clogging waterways in the Great Lakes, Hudson River, and in the Potomac, and upper Bay. It was cleared by mechanical methods in the 1950s, but has reappeared in 1998 in the Bird and Sassafras River, Maryland, and in 2014 in Pohick Bay, Viriginia, on the Potomac. These blooms have been controlled by state agencies, with the help of volunteers.
Image courtesy of U.S. Army corps of Engineers 1977.

Chesapeake Bay Status:

First Record
Regular Resident

Source Region
Native Region
Europe Eurasia

Vector(s) of Introduction
Ornamental(Aquatic Plant)

History of Spread:

Trapa natans (Water Chestnut) has a wide native range in Europe, Asian, and Africa (Cook 1985; Swedish Natural History Museum 2001). The earliest record in North America is cited by Eaton (1947): 'There is a specimen in the herbarium of the New England Botanical Club dated August 29, 1859', from the Sudbury River, Concord MA. It was widely sold by aquarium dealers and planted in fishponds, and in 1884, it was introduced into Collins Lake, in the Hudson River basin in 1884, now abundant in Hudson River from Mohawk River to Rockland County NJ (Mills et al. 1997). Trapa natans spread to the Great Lakes (date not known), probably by a separate introduction, and has required mechanical control in Sodus Bay, Lake Ontario since the 1960's. It is now abundant in the nontidal St. Lawrence and Richelieu Rivers, in Lake Champlain (Mills et al. 1993), and the Connecticut River (Les and Mehrhof 1999).

In the Chesapeake Bay region, Trapa natans has invaded tidal fresh waters of the Potomac River and upper Chesapeake Bay tributaries.

Potomac River - Trapa natans was planted in fishponds in the Washington D.C. as early as 1878, when it was cultivated in a pond by a Department of Agriculture building (U.S. National Herbarium collections). Wild plants were first observed at the mouth of Oxon Run, in the Potomac River in 1923 (Rawls 1964, cited by Stevenson and Confer 1978). The extensive and rapid spread of this plant in the tidal Potomac created navigation problems in the 1920's-30's, with up to 4000 ha of water surface covered, prompting control efforts, including mechanical cutting and herbicides. There was a resurgence in the early 1950's, prompting renewed efforts. 'Many years of control efforts by the Corps of Engineers and expenditures in excess of $550,000 [2.8 million in 1992 dollars; converted from 1950 dollars] has resulted in virtual elimination of Water Chestnut from the Potomac. Only yearly surveillance and hand pulling of isolated plants is now required' (United States Army Corps of Engineers 1977). Plants are now absent or very rare in the Potomac, but seeds are still found in the sediment (Hurley 1990). There are no records from VA, except from the Potomac (United States Army Corps of Engineers 1977), and this plant is not listed in the Atlas of the Virginia Flora (Harvill et al. 1992). In the summer of 2014, a patch of Water Chestnut was discovered in Pohick Bay VA, by Nancy Rybicki (US Geological Survey). The population was harvested by volunteers, organized by John Odenkirk, Virginia Division of Inland Fisheries (Mark Levandowski, personal communication; Interstate Commission on the Potomac River 2014).

Upper Bay and Tributaries - 'In 1955, large patches were found on the Bird River, a Gunpowder River tributary in the Upper Bay. A control program continued for 7 years, but infestations of up to 80 ha reappeared in the Gunpowder and Sassafras Rivers in 1964 and 1965.' After control programs, only a few isolated plants were found (United States Army Corps of Engineers 1977). Trapa natans was not reported in recent submerged aquatic vegetation surveys (Orth 1992) except for one 1987 aerial survey sighting in Sassafras River (Batiuk et al. 1992). However, in 1998, a dramatic resurgence occurred on the Bird and Sassafras River, where colonies covered more than 8 hectares in each river. A mechanical harvester was hired, and many volunteers recruited to remove 1,000,000 kg of plants. In 1999 and 2000, harvest efforts continued, and T. natans' coverage was greatly reduced (Maryland Department of Natural Resources 2000).

History References - Batiuk et al. 1992; Eaton 1947; Harvill et al. 1992; Hurley 1990; Les and Mehrhof 1999; Maryland Department of Natural Resources 2000; Mills et al. 1993; Mills et al. 1997; Orth 1992; Stevenson and Confer 1978; United States Army Corps of Engineers 1977

Invasion Comments:

This data was last modified on Monday, March 16th, 2015.
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