Weeding the Water: LCC Removes Water Chestnut

Gardens were not the only places being weeded in August—LCC hosted a water chestnut removal event with the Vermont Department of Environmental Conservation at the Sandbar Wildlife Management Area in Colchester, VT. Volunteers spent the morning paddling the shallow waters north of the mouth of the Lamoille River and pulling up the invasive plant to help prevent it from colonizing the area.

The European water chestnut, Trapa natans, is an aquatic plant with a submerged, flexible stem whose roots anchor into the mud of shallow lakes, ponds, and slow-moving streams. The stem can extend up to 16 feet toward the surface, where the plant will put out rosettes of glossy, floating, fan-shaped leaves. Each individual plant can produce up to 20 of these rosettes. The flowers grow at the center of the rosette and are solitary, small, white, and four-petaled.

In mid- to late summer the water chestnut will produce large seeds with four sharp orthogonal spines, which change color as they ripen from green to brown. Each rosette can generate 15-20 seeds, giving it a strong ability to spread. Because the water chestnut is an annual plant it depends on these seeds to reproduce – at the end of the summer the seeds fall to the muddy lake or river bottom and can remain viable there for up to 12 years. That is why the timing of harvesting in mid to late summer is crucial.

Water chestnut is extremely competitive in shallow water with soft, muddy bottoms. It creates impenetrable floating canopies across long swaths of the water, often layering as it grows to be up to a foot thick. These mats make previously-fished areas inaccessible, and limit the movement of recreational boats and swimmers. They also restrict light in the water column which in turn limits the growth of native aquatic plants. Unlike these native plants, the invasive water chestnut has little nutritional value to waterfowl and other aquatic organisms. The dying back and decomposition of these mats reduces dissolved oxygen in the water which. can lead to fish kills and other severe negative effects on aquatic organisms.

Water chestnut was first discovered in Lake Champlain in the 1940's south of Crown Point Bridge in the southern reaches of the lake. In more recent years it has been reported further north. The population of water chestnut up at Sandbar WMA is burgeoning, so while our August harvesting did not yield a truckload of plants, these annual hand-pulling efforts are critical to suppress populations in an area where spread control and eradication is still possible.

The Lake Champlain Committee (LCC) has been a long-time supporter of aquatic invasive species funding for state environmental agencies, and has lobbied for a consistent budget to control these invasives. Each time funding has been lost, water chestnut populations have not only increased, but have spread further north.