A mechanical harvester removes tons of water chestnuts from the Nashua River

Fighting Invasive Water Chestnut Infestations

The exotic water chestnut (trapa natans) was first discovered in the Pepperell Pond impoundment on the Nashua River (on the Pepperell/Groton line) in the late 1990’s. At roughly the same time, the plants were found in the Nashua River upstream of Mine Falls Dam in Nashua, New Hampshire.

An impenetrable mat of water chestnuts on Pepperell PondInvasive water chestnut plants create an impenetrable mat of growth that makes the river inaccessible to boating and fishing. Their growth replaces ecologically critical native plant species. When the dense mats die off in the fall, they sink and decay, which depletes oxygen levels vital to fish, destroying native fish habitat with resulting negative impact on fish populations.

As part of its work to maintain water quality, and to protect our waterways for habitat and recreation, the NRWA in early years of the infestation, helped to organize hand-pulling efforts from canoes and kayaks in Pepperell Pond. However, the exponential way in which water chestnut grows (each seed can produce up to 120 new plants) soon deemed hand-pulling ineffective in controlling its spread. By 2005, approximately 45 acres of the Pepperell impoundment were 100% covered in the plant. The NRWA and its partners worked to find funding.

Volunteers harvest water chestnuts by hand - Photo by Ray ManomaitisIn 2008, the Town of Pepperell contracted with the NRWA to manage a grant from the Massachusetts Department of Conservation and Recreation to mechanically harvest the plants. During the summers of 2008 and 2009, approximately 2,780 tons of plants were removed from the river by a private contractor. Because seeds can exist up to 12 years in sediment, harvesting needs to take place continuously for approximately 5 years before the plants can finally be controlled by hand-pulling. Funding for mechanical harvesting has not been available since 2009. NRWA continues to seek sources of funding while hosting hand-pull events with volunteers to check the spread of the plant into new regions. View a slideshow of the 2012 volunteer chestnut pull created by Denise Hurt.

Water chestnut has also taken hold above Mine Falls Dam in Nashua, New Hampshire, and in 2011, approximately 14 acres of the plant covered the area just upstream of the boat ramp at dam. The City of Nashua contracted with Aquatic Control Technologies, Inc. to harvest the plants in August 2011, and plans to continue this effort in subsequent years.

For more information on water chestnuts or hand-pull events or NRWA’s work to control water chestnuts, please contact Martha Morgan, NRWA Water Programs Director, at (978) 448-0299, or This email address is being protected from spambots. You need JavaScript enabled to view it.