European Water Chestnut (EWC) (Trapas natans) is an aggressive invasive aquatic plant that has been detected in the Welland River. The Invasive Species Centre (ISC) is leading a Rapid Response Program to remove EWC from the Welland River with support from the Ontario Federation of Anglers and Hunters (OFAH)  and the Niagara Peninsula Conservation Authority (NPCA). 

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European Water Chesnut

European Water Chestnut (EWC) (Trapa natans) is an invasive aquatic annual plant that was detected in the Welland River in 2020.  

EWC is a prohibited species in Ontario under the Ontario Invasive Species Act (2015). For a species to be listed under the Act, it must have potential to cause harm to Ontario’s economy, environment and society. EWC can cause the following harmful impacts: 

  • Shades out native species and reduces biodiversity 
  • Develops into dense floating mats that can affect various types of recreation such as swimming, fishing, paddling, and boating 
  • Dense mats decompose every year and create anoxic conditions in the river, affecting fish species and species-at-risk like freshwater mussels 
  • Drops sharp seeds that can cover the substrate, slice skin and be painful to step on  
  • Negatively impacts local recreation and related economies 
  • Impacts private river front access and property values 

In 2021, the Invasive Species Centre and Ducks Unlimited Canada paddled the river to assess the population. Fortunately, it was determined that a rapid response effort to manually control the plant would likely contain the population and reduce its spread throughout the Niagara Region and further into Ontario. 

EWC Rapid Response Program

The Plan: Contain and Eradicate  

With support from the Ministry of Northern Development, Mines, Natural Resources, and Forestry (NDMNRF) and the Ontario Federation of Anglers and Hunters (OFAH) Hit Squad Program (via Canada Summer Jobs), the Invasive Species Centre and the Niagara Peninsula Conservation Authority (NPCA) is launching a Rapid Response Program to contain the spread of EWC in the Welland River. The program will aim to contain the population within 4 years. EWC seeds can survive and sprout for up to 10 years so the initial control efforts will be followed by a monitoring and maintenance program.   

Stop seed production 

EWC is an annual plant. Annual plants grow from the previous year’s seed. By removing the plant before it produces seed, the population cannot sustain itself and the number of plants emerging each year declines. Ducks Unlimited Canada and Ontario Parks have been fighting EWC in Eastern Ontario for over 5 years, and they are winning the battle. Ontario Parks recorded 95% reduction in seed viability after 4 years of manual control.  

To stop seed production in the Welland River, the OFAH Hit Squad Team will manually remove (hand-pull) EWC from the river between June 27 and Sept. 2 using canoes and a small motorboat. Biomass will be disposed of at the NPCA properties on the river, Chippawa Creek and E.C. Brown conservation areas.  

Opportunities to Help 

Learn to Identify EWC 

EWC grows from seed settled on the river bottom. Plants emerge in late June and form rosettes on the top of the water. Rosettes are a light, shimmering green measuring up to 30 cm in diameter and can be found in clusters or floating alone.  

EWC will flower in July. Flowers are small and white and appear in the middle of the rosette.  

Each rosette can produce up to 20 seeds per growing season and each stem can have up to 20 rosettes. These seeds can then produce up to 10-12 stems. Mature seeds will drop to the bottom of the river in late August. Some seeds may be transported to other areas by waterfowl or boats.   

Plants will decompose in the fall. There will be no evidence of EWC in the river until the following spring.  

Report Observations on EDDMapS 

  1. Download the EDDMapS Application and create/log in to your account 
  1. Choose to report a new sighting   
  1. Insert:  
  • Species you are reporting   
  • Observation Date  
  • Photos  
  1. Report location or turn on location services. You can edit the report to show your exact location. You can also edit to show infestations by drawing polygons to show the exact spot  
  1. Save and upload to the queue.   

For more information on reporting to EDDMapS

Recreational paddlers are encouraged to ‘Paddle with a Purpose’ this year in waterways across Niagara.

Join the Invasive Species Centre and the NPCA at one of two Paddling Tours to learn how to identify and report EWC observations.  Any additional observations will be managed as funding allows.  Additional observations ensure that the population will be fully contained. No observations suggest that EWC is only in the Welland River.  

The program is offering two paddling tours this year. Both events will launch from E.C. Brown Conservation Area (and paddle west toward Wellandport for ~1.5 km to find the first known population of EWC.  

  • Thursday, July 7, 2022, at 9 a.m.  Register here.  (media kits available)
  • Saturday, July 16, 2022, at 10 a.m. Register here.  

Support the Field Team 

The OFAH Hit Squad Field Team will be on the Welland River removing EWC from June 27 – Sept. 2.  They will be using canoes and one small motorboat. Riverfront landowners are encouraged to support the field team in the following ways: 

  • Provide river access for canoes and/or a small boat on a trailer 
  • Provide emergency exits/shelter in case of inclement weather or health emergency 
  • Offer remote locations for biomass disposal to reduce travel time to Conservation Areas 
  • Provide a place for off-river health breaks 

If you think you can help the team – please contact the program coordinator Karen Alexander ( Your location can be identified with an icon in the Arc GIS Field Map that the team can access on a smartphone. These locations can be anonymous or include your name and contact information.