What Ontario is 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. For more information on the Invasive Species Act and Regulations visit www.ontario.ca/invasionON.
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 at Ottawa, and in the St. Lawrence River at 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 could possibly be the result of a water garden plant(s) being improperly released or boat(s) contaminated with water chestnut being launched in these areas.
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.
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 kills.
Since water chestnut populations occur only in a few locations in Ontario, it is very 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 – 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.
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.
- Avoid infested areas and reduce your speed when travelling near European water chestnut infestations. You must take all reasonable precautions to avoid spreading European water chestnut to new areas of a waterbody.
- Inspect 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 body of water 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 body of water.
- If you have any information about the illegal importing, distribution or sale of European water chestnut, report it immediately to the MNRF TIPS line at 1-877-TIPS-MNR (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 other invasive species in the wild, please contact the toll free Invading Species Hotline at 1-800-563-7711, or visit EDDMapS Ontario to report a sighting.
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