A troublesome old invasive has reared its head once again on the Potomac River. While sampling fish populations, biologists with Virginia Game and Inland Fisheries (VGIF) found a dense clump of water chestnuts, covering about ½ acre of water, near a boat rental dock in Pohick Bay Regional Park, 25 miles south of the nation’s capital.
Response was quick, as VGIF organized volunteers to hand pull the troublesome plant this past fall.
“Water chestnut is probably a lot more troublesome and invasive potentially than snakeheads might be,” said biologist John Odenkirk.
“It was dense, but we got it. Hopefully, we nipped the potential for this plant to take over the bay and shut it down.”
Because it is an annual that sprouts from seeds, this fast-growing exotic is not susceptible to herbicides. It can be controlled only by pulling or mechanical harvest. The seeds have sharp needles that can attach to wildlife, clothing, and other items for transport to new areas, and they can remain viable in sediment for more than a decade. Just one acre of plants can yield enough seeds to cover 100 acres.
Native to both Asia and Europe, water chestnut was first confirmed on the Potomac in 1923, with a two-acre bed expanding to cover 41 miles of river, from Washington, D.C., to near Quantico, Va., in just two years. According to the U.S. Geological Survey (USGS), the dense, floating mats restricted navigation, harmed fisheries, and killed off submersed plants with their thick canopy.
The Army Corps of Engineers mechanically harvested the infestation and the plant was considered mostly eradicated from the Potomac by 1945. But limited hand harvesting continued into the 1960s.
USGS is studying this more recent invader to determine its species and lineage. Its spiny seed pods don’t resemble those of water chestnuts found in Maryland and other states. Additionally, VGIF and volunteer stewards will keep an eye out for future outbreaks.