SAV watershed brackish

Background

Water Chestnut (Trapa natans) is an aquatic plant native to Europe, Asia and Africa. The introduction of the water chestnut to the eastern United States is thought to have occurred during the 1870s. The plant is known to have ornamental and medicinal value, and was cultured by Harvard botanist Asa Gray. Water chestnut grows in nutrient-rich shallow lakes and rivers. It consists of a submerged floating stem that attaches to a buoyant rosette of leaves.

The water chestnut's flowering season begins in June and continues into mid-July. The water chestnut fruit is a caltrop-shaped nut with four half-inch barbed spines. The seeds can remain viable for up to 12 years, although most will germinate within the first two years. Once germinated, the water chestnut plantlet develops at a rapid rate. Each water chestnut seed can produce up to 15 to 20 new rosettes and each rosette can generate up to 20 seeds. The prolific plant can cover a given area with a dense mat of vegetation, which causes significant damage to the health of a water body's ecosystem.

The Problem

• Water chestnut colonization creates a canopy that interrupts the passage of light through water, which is necessary to maintain a well-functioning ecosystem.
• Water chestnut colonies crowd out and alter the habitat of many native species.
• The dense mats created by water chestnut colonies block navigable waterways for boaters.
• The water chestnut seed is a danger to bathers and beachcombers, its hard spikes capable of tearing through shoe leather

The Solution

Water chestnut infestations occur in isolated areas. Currently populations exist on the Sassafras and Bird rivers of Maryland, and in a number of ponds, including a nontidal pond above Lloyds Creek and in Urieville Lake in Kent County, Maryland. Maryland has been active in efforts to remove the water chestnut since the 1960s. Water chestnuts can be removed by hand and or using mechanical harvesting methods. The Maryland Department of Natural Resources has run a harvesting program since 1999 which has focused on the water chestnut populations on the Bird and Sassafras rivers.

Water Chestnut photo courtesy: U.S. Fish and Wildlife Service

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Last modified: 11/7/05