On March 23, 20206, the U.S. Army Corps of Engineers, Baltimore District (USACE), released a draft Integrated Letter Report and Programmatic Environmental Assessment (EA) for the long-term, regional management of the invasive water chestnut. Federal participation in this action is through the USACE Aquatic Plant Control Program. The draft EA evaluates the potential environmental effects of managing two invasive aquatic plants, including the two-horned water chestnut (Trapa bispinosa) and the Eurasian water chestnut (Trapa natans), throughout Maryland, Washington, D.C., and Virginia.

• Draft Integrated Letter Report and Programmatic Assessment (EA)
• Related Public Notice 

The draft EA has been prepared in accordance with the National Environmental Policy Act of 1969 (NEPA), as amended. Under the proposed federal action, USACE would enter into a cost-shared agreement with the Metropolitan Washington Council of Governments (MWCOG), the non-federal sponsor, to support ongoing management of these species. Management measures would include manual removal, mechanical harvesting, and targeted herbicide applications to reduce the spread of the invasive plants. Implementation of management activities is anticipated to begin in the summer of 2026.

Adverse impacts to local residents and recreational users at affected water bodies targeted for this work are anticipated to be minimal and temporary. In the long term, the work will have positive effects by reducing the spread of water chestnut, enhancing access for recreational activities, and improving water quality and aquatic habitat within affected water bodies. Based on the preliminary findings in the draft EA, USACE prepared a draft Finding of No Significant Impact (FONSI) located in the referenced draft document.

Public comments will be accepted through April 21, 2026. Comments may be submitted using the fillable form below, or by emailing the Project Manager Jacqueline Seiple at jacqueline.a.seiple@usace.army.mil. 

The U.S. Army Corps of Engineers’ (USACE) Engineer Research and Development Center (ERDC), in cooperation with the Virginia Department of Wildlife Resources (DWR), conducted a demonstration project at Lake Brittle, Virginia, to evaluate the effectiveness of three U.S. Environmental Protection Agency (EPA)-approved aquatic herbicides, flumioxazin, imazamox, and florpyrauxifen-benzyl, in controlling the invasive two-horned water chestnut. 

Treatment was conducted early summer 2025 prior to flowering of the two-horned water chestnut to prevent mature seed production. 

Lake Brittle was selected as the preferred alternative site in collaboration with Virginia DWR to deploy an early detection-rapid response multi-agency approach with the goal of eradicating T. bispinosa var. iinumai in Virginia.

The results were used to determine the most effective herbicide, best treatment timing, potential effects on non-target species, and proper herbicide exposure times. Findings will inform future management practices and will be shared with state, regional, and local agencies, as well as nonprofits, to support broader efforts to control two-horned water chestnut in Virginia and Maryland.

Two-horned water chestnut (Trapa bispinosa) is an annual aquatic plant found in freshwater habitats, typically in still or slow-moving water. Native to East Asia (Taiwan, Japan, China, and Korea), it was first reported in the U.S. in 2014 in Pohick Bay on the tidal Potomac River near Lorton, Virginia. Initially mistaken for Eurasian water chestnut, it was later confirmed to be a genetically distinct species.

In late May, its triangular, serrated leaves begin to emerge on the water’s surface, forming rosettes. These floating leaves are green on top and reddish underneath. The plant’s roots can anchor in sediment in water up to 15 feet deep, and its petioles contain air pockets that help it float. By June, light pink flowers bloom near the center of each rosette and develop into two-horned fruits (seeds).

The plant dies back after the first frosts in November, but its seeds can remain viable in sediment for at least two years.

The plant’s hard, spiny seed pods are notorious for clinging to waterfowl, boats, nets, clothing, and construction equipment. It has been documented in Virginia’s Fairfax, Fauquier, Prince William, and Loudoun counties, and Maryland’s Prince George’s County.

This invasive species is not only disrupting ecosystems but also threatening our ability to safely enjoy our local waterways. Awareness and early intervention are key to stopping its spread.

Two-horned water chestnut forms dense mats on the water’s surface, limiting sunlight, suppressing the growth of native aquatic plants, and reducing oxygen exchange. These effects contribute to declining water quality and threaten aquatic life. It spreads rapidly and can dominate habitats, impacting recreational use of waterways like boating, fishing, and swimming.

Adverse impacts to local residents and recreational users at affected water bodies targeted for this work are anticipated to be minimal and temporary. In the long term, the work will have positive effects by reducing the spread of water chestnut, enhancing access for recreational activities, and improving water quality and aquatic habitat within affected water bodies.