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Invasive Plant Threatens Lake Simcoe

August 20, 2025

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By Angie Sullivan

Cook’s Bay in Lake Simcoe has been infested with a dangerous invasive aquatic plant known as water soldier. The sharply serrated leaves of this plant can shred human skin and choke native vegetation.

Judy Dwyer of Keswick told CBC News that she has been overrun by the plants. “I worked all afternoon pulling it out, and it is back again. I have grandchildren, and you love to see children in the water, but I am afraid for them to come in now.”

Clumps of water soldier were first detected last summer in Lake Simcoe. Robert McGowan is a project specialist of the Invading Species Awareness Program from the Ontario Federation of Anglers and Hunters Foundation. “Water soldier was detected in Lake Simcoe in July of 2024. The Water Soldier Working Group has been on Cook’s Bay monitoring for the plant to delineate the population to determine how much water soldier there is, this will help to inform management strategies. The Working Group has also been conducting surveillance on the main body of Lake Simcoe but have not found water soldier outside of Cook’s Bay to date,” he said.

Sinem Connor, the senior communications advisor from the Lake Simcoe Region Conservation Authority, provided this statement: “Efforts to manage water soldier in Lake Simcoe are underway. These efforts are being led by the Invasive Species Centre with support from provincial and federal government agencies, the First Nation communities of Rama and Georgina Island, the Conservation Authority, community groups, and members of the public. This summer, the focus is on mapping the extent of the invasion and developing the multi-year management strategy.”

“Ontario is working to prevent the spread of water soldier, and other invasive species that threaten our lakes, rivers and local ecosystems. If left unchecked, water soldier has the potential to also have economic impacts and hurt recreation and tourism,” says Mike Harris, minister of natural resources. “That’s why we’re collaborating with the working group members to assess the extent of this invasion and develop plans to help manage it. But everyone can help, by spotting and pulling water soldier when possible, and reporting sightings. By working together, we can protect our waters and local economies.”

Once settled, water soldier spreads aggressively, forming dense floating mats that choke native vegetation and drastically reduce biodiversity. These thick colonies alter water quality and chemistry, with potential consequences for delicate phytoplankton and other foundational aquatic life. The Ontario government has designated water soldier as a prohibited invasive species.

“Water soldier is an invasive aquatic plant that can spread quickly. It is known to alter shallow water habitats by crowding out native plants and impacting living space for fish species,” says Brian Ginn, limnologist for the Lake Simcoe Region Conservation Authority. “If not properly managed, it could have significant effects on both the ecology of Lake Simcoe and our recreational use of the lake.”

Please remember to clean, drain, and dry boats and gear after water use, avoid transporting aquatic plants, properly dispose of unwanted aquarium specimens, and report sightings via the Invading Species Hotline (1-800-563-7711).