The European Water Chestnut (Trapa natans) is a rooted aquatic plant that can take over ponds, shallow lakes and rivers. This invasive aquatic plant species is inadvertently released into water bodies of the Northeast, spreading throughout New England and the Mid-Atlantic states including Pennsylvania, changing aquatic habitats and clogging waterways and ponds. The water chestnut is native to Asia, Europe, and Africa. It was first discovered in North America close to Concord Massachusetts in 1859. In its native habitat, the plant is kept under control by native insect parasites.

Water gardeners brought water chestnut to the United States. It reproduces very quickly and produces up to 15 nuts that contains only one seed in each nut per season. These nuts have sharp spines that can stick to other objects, birds, animals or spread vegetatively. The leaves float and break off into small pieces attaching to boats or drifting to new areas.

European water chestnut is an aquatic plant that has roots with floating and submersed leaves. The submersed leaves develop feathery coils around the stem. Floating leaves are green, shiny, triangular shaped, with a jagged edge that curl into rosettes around the end of the stem, and a single small white flower in the center of the rosette. The stems are spongy and light and can grow up to 16 feet long.

Water chestnut starts flowering and forms seeds in the middle of July and will continue throughout fall until the winter frost kills the rosettes. Each nut that sinks to the bottom of the water body can grow into a new plant. Most of seeds will germinate within the first couple of years, but they can stay viable for up to 12 years. They grow in freshwater, preferably slow-moving water like ponds less than 16 feet deep that is rich with nutrients.

Water chestnut is an annual and at the end of the growing season it dies back. Seeds germinate during springtime. Dense, nut-like seeds start to develop in July. The walnut sized fruits grow under water and have four sharp spikes can pierce through footwear. Nuts that are older, black in color, and float in the water are no longer viable.

Firm floating mats of water chestnut can suffocate a water body and restricting light and oxygen. The colonies change habitats and dominate the aquatic ecosystem by out competing native organism for nutrients and space. Water chestnut doesn’t offer a lot of nutritional value in comparison to beneficial native plants. An infestation can clog water waterways, effecting fishing, boating, and swimming. It is also expensive and hard to keep under control. The main economic costs are associated with chemical and mechanical control. For example, Vermont spent nearly half a million dollars in the year 2000 to remove water chestnut with the use of manual removal and mechanical harvesters.

Water chestnut is an annual plant, so control requires prevention of plants blooming and setting seeds. It’s important to use care while removing water chestnut because fragments can form into new plants. Using the combination of chemical, mechanical, and manual methods is usually the most effective way to keep water chestnut under control. A bigger infestation will require the use of aquatic herbicides, mechanical harvesters, and monitoring for 5 to 12 years to rid of the invader, and complete eradication might not ever be achieved. Early detection is the trick to water chestnut control. Spotting small populations while they are easy to remove by hand is very important. If you notice water chestnut, remove it and dispose of it far away from the water. Each plant removed will prevent up to 120 new plants from growing the next season!