What is Ontario Doing?

To prevent the further spread and introduction of this unwanted invader in the province, Ontario has regulated European water chestnut as prohibited under the Invasive Species Act, 2015. For more information on the Invasive Species Act and Regulations, visit www.ontario.ca/invasionON.

The Ontario Ministry of Natural Resources and Forestry has developed a prevention and response plan to enable people and organizations to undertake low risk activities to monitor, control, and in some cases eradicate these invasive plants without the need for an authorization under the Invasive Species Act, 2015. The plan also includes detailed best management practices for European water chestnut.

To view the prevention and response plan for European water chestnut, follow this link: European Water Chestnut Prevention and Response Plan PDF

Background

European water chestnut (or water chestnut) is an invasive aquatic plant that has been introduced to the Ottawa River in eastern Ontario within Voyageur Provincial Park.  It has also been found at Wolfe Island in Lake Ontario, in the Rideau River in Ottawa, and in the St. Lawrence River in Kingston.  The plant is native to Europe, Asia, and Africa, and is used in North America as an ornamental water garden plant.  Although it’s not certain how the plants arrived in Ontario, it was most likely introduced through the improper release of water garden plants.

Range

Water chestnut was introduced into North America sometime before 1879 by a gardener at the Cambridge Botanical Garden in Massachusetts. Since then, water chestnut has spread to other states in the northeast. It has also been found in Quebec, and in tributaries of the Niagara River and Lake Ontario in New York State. The localized populations in the Ottawa River, and eastern Ontario, are the only known populations in Ontario.

For an up to date distribution map of European water chestnut in Ontario, visit EDDMapS.org/Ontario/distribution.

Impacts of European Water Chestnut

Water chestnut populations in the Ottawa River, as well as neighbouring provinces and states, have become a serious nuisance causing a number of impacts, including:

  • Forms extremely dense floating mats of vegetation that shade out native vegetation, decreasing plant biodiversity and making recreational activities like swimming, angling, and boating almost impossible in the infested areas.
  • The hard nuts with sharp, barbed spines can accumulate on shore and cause injury when stepped on.
  • Reduced light penetration and plant growth beneath the water chestnut canopy, combined with a large amount of decomposing vegetation below, can lead to decreased dissolved oxygen levels, which can impact native species and cause fish deaths.

Since water chestnut populations occur only in a few locations in Ontario, it is important that we put every effort towards removing this plant before it spreads to other locations. The Ministry of Natural Resources and Forestry, with support from partnering agencies, are working to eradicate water chestnut from the Ottawa River by pulling the plants by hand, with rakes, and mechanical harvesters. Efforts to control this new invader are ongoing.

How to Identify European Water Chestnut

Water chestnut has an appearance unlike any other plant species in Ontario. Features that can be used to identify water chestnut, include:

  • Floating leaves.
  • The leaves are leathery, bright green, grow up to 5 cm wide, and are diamond- or fan-shaped with sharply toothed edges.
  • The leaves form a densely crowded rosette up to 30 cm in diameter.
  • The leaf stems are up to 15 cm long, with a spongy swollen section that helps the plant float.
  • Underwater leaves are feather-like with finely dissected leaf segments.
  • The flowers are very small (8 mm long), white, and have four petals
  • Produces a hard “woody” nut (seed), 3 to 4 cm wide with sharp barbed spines. Viable seeds have a fleshy green outer layer and sink to the bottom. Older seeds are black, floating, with four sharp barbed spines and are not viable.
  • The nuts bear no resemblance to the “water chestnut” used in Asian cooking, nor are they edible.

What You Can Do

  • Learn how to identify European water chestnut and how to prevent accidentally spreading the plant with your watercraft or fishing equipment. This is especially important if you are planning to do work or participate in recreational activities in infested areas of the Ottawa River or other areas that contain European water chestnut.
  • Never buy or keep European water chestnut in your water garden or aquarium. It is against the law to buy, sell, trade, possess, or transport European water chestnut.
  • Clean, Drain, Dry your boat, trailer, and equipment after each use. You must remove all European water chestnut, or parts of these plants, and dispose of them in the garbage or away from any waterbody before transporting your boat over land.
  • Never deposit unwanted aquarium or water garden plants into Ontario lakes or rivers. Dispose of them in the garbage or away from any waterbody.
  • If you have any information about the illegal importation, distribution, or sale of European water chestnut, report it immediately to the MNRF at 1-877- 847-7667, toll-free anytime. You can also call Crime Stoppers anonymously at 1-800-222-TIPS (8477).
  • If you’ve seen European water chestnut or another invasive species in the wild, please contact the toll free Invading Species Hotline at 1-800-563-7711, visit EDDMapS Ontario, or search for the ‘Invasive Species in Ontario’ project on iNaturalist.org to report a sighting.

Gallery


OFAH/OMNRF Invading Species Awareness Program. (2012). European Water Chestnut. Retrieved from: www.invadingspecies.com.
This factsheet may be reproduced for non-commercial purposes.

Header photo by Ontario Federation of Anglers and Hunters