About Aquatic Invasive Species

YG photo

What Do I Need to Know?


What are aquatic

invasive species?

  • Introduced aquatic organisms that can harm native species by bringing disease and altering ecosystems. This impacts fisheries, tourism, health, and recreation.

Full definition of an invasive species:

An organism (plant, fungus, or bacterium) that is introduced into an ecosystem and has negative effects on the economy, environment, and/or health. The term “invasive” is reserved for the most aggressive species, which reproduce rapidly and cause major changes to the areas where they become established.
                                                              – Yukon Invasive Species Council


How are aquatic invasive species spread?

  • Mostly by people and their equipment when they move from place to place. For example:
  • During water-based activities like fishing, aquatic organisms can cling to boats, fishing gear, and footwear;
  • Illegal dumping of aquariums.


Are there aquatic invasive species in Yukon?

  • We don’t know. Most Yukon lakes and waterways appear to be free of invasive species.
  • The algae, didymo, is in Yukon, but we don’t have a good understanding of where it’s found and whether it’s spreading. Didymo is considered invasive elsewhere, but may in fact be native to Yukon.
  • Some species of fish have been introduced to Yukon waters but are not considered invasive at this point in time (rainbow trout, stickleback, Arctic char, and goldfish)


What aquatic invaders should I look out for?

  • Zebra and quagga mussels
  • Didymo algae

Zebra and Quagga Mussels

Left: Zebra mussel (photo by Amy Benson, U.S. Geological Survey, Bugwood.org). Right: Quagga mussels (photo by David Britton)


Zebra and quagga mussels attach to boat hulls and underwater infrastructure, and can cost millions of dollars of damage. Adult mussels can live several weeks out of the water and be easily transferred from one body of water to another.

How to identify zebra and quagga mussels:

  • Usually fingernail-sized (less than 5 cm)
  • Look like D-shaped clams with yellow or brownish shells and light-coloured stripes
  • Only freshwater mussels that attach themselves firmly to solid objects

This YouTube video of Silent Invaders explains how these mussels infest lakes.

Didymo Algae

                                                                   (YG photo)

We know didymo is in Yukon, but we don’t have a good understanding of where it’s found and if it’s spreading. Didymo algae can be invasive and form large, slippery mats that cover streambeds. These mats can degrade fisheries and the aquatic ecosystem by changing benthic invertebrate communities and affecting fish rearing habitat. As stream levels drop, didymo is sometimes mistaken for toilet paper. Didymo can affect the aesthetics of lakes and streams.

How to identify didymo algae:

Not Didymo
Looks like: Range in colour from brownish-yellow to white, in clumps or ropes Green or dark brown/black, transparent
Feels like: Rough texture like wet cotton wool when pulled apart Slimy texture, falls apart when handled
Found: In clumps on rocks or plants, or floating in the current Attached to the bottom with roots


This YouTube video produced by New Zealand Fish & Game explains how didymo can form large algal blooms.


Fish and Wildlife, Fisheries

Environment Yukon

Government of Yukon

Box 2703 (V-5A)
Whitehorse, Yukon
Canada Y1A 2C6

Phone: 867-667-5721
Toll free (in Yukon): 1-800-661-0408 ext. 5721
Fax: 867-393-6263

Email: fisheries@gov.yk.ca