Invasive plant that can cut swimmers with saw-like teeth spreading in Ontario

A harmful invasive plant species has been spotted in Ontario's waters once again this year, raising concerns among environmental officials over its impact on local ecosystems and recreational activities. 

Water soldier (Stratiotes aloides) is a perennial aquatic plant native to Europe and northwest Asia. The plant was recently detected in Lake Simcoe's waters for the first time last year, and its appearance in Cook's Bay is among a small number of confirmed populations in the province, which also includes the Trent River, the Bay of Quinte, and a few lakes in eastern Ontario. 

Before it was regulated under Ontario's Invasive Species Act as a prohibited species, water soldier was sold for ornamental use in water gardens, which was most likely the pathway for its introduction to the wild. 

Photo: Victoria Tucholka/Shutterstock.com.

The pesky plant species poses multiple environmental and recreational concerns, as it forms dense mats of floating vegetation, which outcompete native plant species and reduce biodiversity. The plant can also alter water chemistry, potentially harming phytoplankton and other aquatic organisms. 

Its thick mats obstruct boating, angling, and swimming, and its sharp, serrated leaves can injure you while you swim or if you unwittingly handle the plant. The species is similar in appearance to an aloe vera or spider plant, forming a bright green rosette of sword-shaped leaves up to 40 centimetres in length. 

Photo: bykot photo/Shutterstock.com.

Its leaves are edged with sharp spines, which is a key feature that distinguishes it from other aquatic plants like bur-reeds, arrowheads, or eel-grass. Typically submerged, water soldier becomes buoyant during the summer months. As the leaves start to mature, they become waterlogged, and the plant sinks below the water's surface. 

Although the species can flower, with small white blooms of three petals, this is exceptionally rare in Ontario. 

To help prevent its spread, officials advise avoiding infested areas or reducing boat speed near them, as the wake can dislodge the plant and help it spread. If you're out on a boat, make sure to regularly inspect and clean it, ensuring that after each use, no plants, mud, or aquatic organisms are transported between water bodies. 

If you come across the species this summer, make sure to report sightings to the Invading Species hotline 1-800-563-7711 or visit Ontario's Invading Species Awareness Program.