What Ontario is doing

To prevent this unwanted invader from coming into the province, Ontario has regulated floating primrose-willow (Ludwigia peploides) as a restricted invasive species under the Invasive Species Act.

Learn about the Invasive Species Act and regulations.

Background

Floating primrose-willow, also known as creeping primrose-willow, is a herbaceous perennial aquatic plant that thrives in shallow waters of wetlands, ponds and slow-moving streams. This invasive plant forms dense mats on the water’s surface, impeding water flow and crowding out native species.

While no longer permitted in Ontario, floating primrose-willow is sometimes used in ornamental water gardens and aquaria. It may be introduced to natural areas through the improper disposal of water garden or aquaria contents. In areas where floating primrose-willow becomes established, it can easily spread due to its rapid vegetative reproduction. Pieces of stems can spread by:

  • flowing water to connected waterbodies
  • wildlife or human activities
  • the movement of boats and equipment
  • its use in water gardens

Range

Floating primrose-willow is native to South America and the southeastern United States. It has spread to other parts of the world, including several northern U.S. states and Europe.

In Canada, it has been primarily found in southern regions where the climate is warmer, including parts of British Columbia and the Lake Erie St. Clair basin in Ontario.

View an up-to-date distribution map of floating primrose-willow.

Impacts of floating primrose-willow

Floating primrose-willow forms thick mats of vegetation on the water’s surface which can alter aquatic ecosystems by shading out other aquatic plants. It can disrupt ecosystem processes and reduce biodiversity by lowering dissolved oxygen levels, increasing water acidity and sedimentation. These dense colonies also impede recreational activities such as boating, swimming and fishing.

How to identify floating primrose-willow

Floating primrose-willow has bright yellow flowers, 1 to 1.5 cm long, with 5 or 6 petals each, and usually blooms in late July to August. It has fleshy hairless or slightly haired stems with a reddish colour that float on the water's surface or creep along the ground. The alternately arranged leaves are dark green with smooth margins. They are elongated and egg to spear shaped and grow up to 8 cm long.

What you need to know

  • Learn how to identify floating primrose-willow and prevent its introduction or spread in Ontario’s waterways.
  • It is illegal to:
    • possess or transport floating primrose-willow in a provincial park or conservation reserve
    • bring floating primrose-willow into Ontario
    • deposit, release or propagate floating primrose-willow, including planting it or any other actions which may encourage its spread or growth
    • buy, sell, lease or trade floating primrose-willow in Ontario
  • Never keep or grow floating primrose-willow 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 them 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 importation, distribution, or sale of floating primrose-willow, report it immediately to either:

If you’ve seen floating primrose-willow or another invasive species in the wild, please: