What Ontario is doing

To prevent this unwanted invader from spreading in the province, Ontario has regulated Eurasian water-milfoil (Myriophyllum spicatum) as a restricted invasive species under the Invasive Species Act.

Learn about the Invasive Species Act and regulations.

Background

Eurasian water-milfoil is a submerged perennial aquatic invasive plant. It can be found in a range of water conditions from fresh to brackish, alkaline to acidic and even in nutrient-poor waters. Eurasian water-milfoil thrives in still or slow-moving waterbodies.

The plant was likely first introduced from the ballast water of Trans-Atlantic shipping vessels to the northeastern United States between the late 1800s and 1940. Eurasian water-milfoil was first discovered in Canada in Lake Erie in 1961. It has since spread throughout the Great Lakes, the St. Lawrence River and many inland lakes of Ontario and Quebec.

Given its ability to reproduce from small plant fragments, Eurasian water-milfoil is easily spread through various pathways including:

  • contaminated watercraft and equipment
  • connected waterbodies
  • fishing gear
  • improper disposal of aquaria or water garden contents

Range

Eurasian water-milfoil is native to Europe, Asia and North Africa. It has been introduced and has become invasive in many parts of the world, spreading across every continent except Antarctica.

In Canada, Eurasian water-milfoil has spread to all the Great Lakes, the St. Lawrence River and many inland lakes throughout Southern and Central Ontario, as well as Quebec.

View an up-to-date distribution map of Eurasian water-milfoil.

Impacts of Eurasian watermilfoil

The rapid growth of Eurasian water-milfoil can form dense mats on the water's surface. These mats can:

  • displace native aquatic plants and reduce biodiversity
  • interfere with recreational activities like swimming, fishing and boating

 

  • deplete oxygen levels, which can impact fish and other aquatic organisms
  • create stagnant water increasing habitat for mosquitoes

How to identify Eurasian water-milfoil

Eurasian water-milfoil has long, feathery leaves, typically arranged in groups of 3 to 5 leaves around the stem. Each leaf is finely divided, usually having 12 to 21 pairs of threadlike leaflets. The plant has a slender, branching stem that can grow up to 3 metres long. The stems are often reddish-brown to pink but can sometimes appear green. During its flowering stage, usually in late spring to early summer, it produces small reddish flowers on a spike that rise above the water's surface. These spikes can be about 4 to 8 centimetres long.

Although Eurasian water-milfoil can be difficult to distinguish from the native Northern water-milfoil, the native milfoil typically has fewer leaflet pairs (usually less than 10), remains rigid when taken out of the water and does not form the thick vegetative mats characteristic of Eurasian water-milfoil. However, Northern water-milfoil and Eurasian water-milfoil can hybridize, causing the plant’s physical characteristics to mix.

What you need to know

  • Learn how to identify Eurasian water-milfoil and prevent its introduction or spread in Ontario’s waterways.
  • It is illegal to:
    • possess or transport Eurasian water-milfoil in a provincial park or conservation reserve
    • bring Eurasian water-milfoil into Ontario
    • deposit, release or propagate Eurasian water-milfoil, including planting it or any other actions which may encourage its spread or growth
    • buy, sell, lease or trade Eurasian water-milfoil in Ontario
  • Never keep or grow Eurasian water-milfoil in an aquarium, water garden or for any other purpose.
  • Always clean, drain and dry your watercraft before transporting it to another waterbody.
  • As of January 1, 2022, boaters must open or remove drain plugs and other devices to allow water to drain. They must also take reasonable measures to remove plants, animals and algae from their watercraft, watercraft equipment and trailer before transporting it overland.
  • Boaters must ensure watercraft, watercraft equipment and trailers do not have aquatic plants, animals or algae attached to them before arriving at a launch site or placing the watercraft into any waterbody.

 

Reporting illegal activity

If you have any information about the illegal distribution or sale of Eurasian water-milfoil, report it immediately to either:

If you’ve seen Eurasian water-milfoil or another invasive species in the wild, please: