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Water Fern

Genus Azolla
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What is Ontario Doing?

To prevent this unwanted invader from coming into the province, Ontario has regulated genus Azolla as restricted under the Invasive Species Act, 2015 


The genus Azolla includes seven species of aquatic floating ferns such as large mosquitofern (A. filiculoides) Carolinian mosquitofern (A. caroliana), and feathered mosquitofern (A. pinnata). Azolla spp. reproduce vegetatively when fragments from the main axis break off. Azolla spp. can fix nitrogen through a symbiotic relationship with cyanobacteria, which is why it is often used to aid in fertilizing rice paddies in southeast Asia.


In Canada, Azolla is at risk of being released into the wild from water-garden escapees and releases. The plant thrives in warm, slow-moving waterbodies and can fragment easily and spread to new areas.

Impacts of Genus Azolla

  • Can easily spread from waterbody to waterbody and grows aggressively to compete with native plants.  
  • Forms dense mats of floating vegetation, blocking available sunlight, reducing water quality and removing fish habitat.  
  • Mats can dislodge and cause stagnant waters as they decompose, killing native plants and animals. 
  • Dense mats can hinder recreational activities such as boating, angling and swimming. 

How to Identify

  • Individual plants are small and consist of a short, branched, floating stem with alternatively arranged leaves. 
  • Reduced in form, do not represent typical “ferns” but rather resemble duckweed or mosses. 
  • Some species have a reddish colour to their leaves, giving a striking red colour to the surface of waterbodies they have infested. 

What You Can Do

  • Learn how to identify Azolla spp. and how to prevent the introduction or spread of this plant.  
  • Never buy, plant, or keep Azolla spp. in your aquarium or water garden. It is against the law to buy, sell, trade, possess, or transport Azolla spp.  
  • Never deposit unwanted aquarium or water garden plants into Ontario’s lakes or rivers. Dispose of them in the garbage or at least 30 metres away from any waterbody.  
  • Clean, Drain, Dry your boat, trailer, and equipment after each use, be sure to remove all plants, animals, and mud before moving to a new waterbody.  
  • If you have any information about the illegal importing, distribution, or sale of Azolla spp. , report it immediately to the MNRF at 1-877-847-7667, toll-free anytime. You can also call Crime Stoppers anonymously at 1-800-222-TIPS (8477).  


OFAH/OMNRF Invading Species Awareness Program. (2023). Genus Azolla. Retrieved from:
This factsheet may be reproduced for non-commercial purposes.

Header photo ‘Azolla Caroliniana’ by KrzysztofZiarnek,Kenraiz | WikiMediaCommons 

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