What Ontario is doing

To prevent this unwanted invader from coming into the province, Ontario has regulated oxygen weed (Lagarosiphon major) as a prohibited invasive species under the Invasive Species Act, 2015.

Learn about the Invasive Species Act and regulations.

Background

Oxygen weed, also known as African elodea, is a perennial aquatic invasive plant native to South Africa.

Oxygen weed prefers clear, cool temperate waters with direct sunlight where it can grow to depths of 6.6 metres. In murky waters it only grows to about 1 metre. It can survive in a range of nutrient levels, but its abundance declines due to low water clarity in nutrient rich waters.

While no longer permitted in Ontario, oxygen weed is sometimes used in aquaria and ornamental water gardens (backyard ponds). Improper disposal of aquaria or escape from water gardens are the main pathways for its introduction to a new area.

Once established, it can spread rapidly through connected waterbodies, hitchhiking on boats or equipment which have not been cleaned.

Even a small plant fragment introduced to a new area can start a population, which is why it’s so important to clean watercraft and equipment before transporting to a new area.

Range

  • Native to Africa.
  • Introduced and present in Europe, Australia, New Zealand and the United Kingdom.
  • Not currently known to be present in the wild in Canada or the United States.

Learn about the distribution of oxygen weed.

  Impacts of oxygen weed

  • Creates dense mats of vegetation which can restrict sunlight and lead to decreased native species abundance and biodiversity.
  • Decomposing plants can create low levels of oxygen in the water potentially leading to fish kills.
  • Negatively impacts recreational activities such as boating and swimming.
  • Extensive growth can block the intake screens of hydro-electric power stations and other industrial water intake applications.

How to identify oxygen weed

Oxygen weed can be identified by:

  • submerged, long stems with bright green, feathery, and finely divided leaves which can grow up to several metres in length
  • leaves arranged in whorls (meaning leaves grow in a circle around the stem), giving the plant a distinctive and lush appearance beneath the water's surface.
  • in rare cases, small white or pale pink flowers on long stalks that extend above the water's surface

What you need to know

  • Learn how to identify oxygen weed and how to prevent the introduction or spread of this plant into local waterways.
  • It is against the law to import, possess, deposit, release, transport, breed, grow, buy, sell, lease or trade oxygen weed in Ontario.
  • Never release plants into the natural environment. This can unintentionally start an invasion that will negatively affect Ontario’s native species.
  • Never buy or grow oxygen weed to use in an aquarium, water garden, or for any other purpose. Always clean, drain and dry your watercraft if removing it and 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 importation, distribution or sale of oxygen weed, report it immediately to either:

If you’ve seen oxygen weed or another invasive species in the wild, do one of the following: