Species At Risk

Rainbow Mussel

(Villosa iris)


Rainbow Mussel


The Rainbow Mussel is a small freshwater mussel that usually grows to eight centimetres long. The shell is yellow, green, or brown on the outside. The inside of the shell is iridescent giving this species its name. The Rainbow Mussel can be distinguished from other Ontario mussels by its elongated oval-shaped shell that has many broken, dark green lines. It also has the unique ability to produce a fishing lure that looks and moves like a crayfish.

Action we are taking:


In Canada, the Rainbow Mussel is found only in Ontario in the Ausable, Bayfield, Detroit, Grand, Maitland, Moira, Niagara, Salmon, Saugeen, Sydenham, Thames and Trent rivers and in Lake St. Clair. It may no longer exist in the St. Clair, Detroit and Niagara rivers, and Lake Erie.


The Rainbow Mussel prefers small to medium-sized rivers with a moderate to strong current and sand, rocky, or gravel bottoms. It is found in or near riffle areas and along the edges of vegetation in water less than one metre deep. All mussels filter water to find food, such as bacteria and algae. Mussel larvae must attach to a fish, called a host, where they consume nutrients from the fish body until they transform into juvenile mussels and then drop off. The Rainbow Mussel uses a variety of fish hosts in Ontario, including Striped Shiner, Smallmouth Bass, Largemouth Bass, Green Sunfish, Greenside Darter, Rainbow Darter, and Yellow Perch.


The invasive Zebra Mussel is a serious threat to the Rainbow Mussel. This invasive species from Europe attaches to other mussels and can kill them by interfering with breathing and feeding. Agriculture and urban development can also threaten this species by adding sediment, nutrients and contaminants into waterways that reduce water quality.


The Rainbow Mussel is protected under Ontario’s Endangered Species Act.

What You Can Do to Help the Rainbow Mussel

  • The Ministry of Natural Resources tracks species at risk such as the Rainbow Mussel. You can use a handy online form to report your sightings to the Natural Heritage Information Centre. Photographs with specific locations or mapping coordinates are always helpful. nhic.mnr.gov.on.ca
  • Report any illegal activity related to plants and wildlife to 1-877-TIPS-MNR (847-7667).
  • Invasive species seriously threaten many of Ontario’s species at risk. To learn what you can do to help reduce the threat of invasive species, visit: ontario.ca/invasivespecies ; www.invadingspecies.com ; www.ontarioinvasiveplants.ca ; and, www.invasivespecies.gc.ca .
  • Volunteer with your local nature club or provincial park to participate in surveys or stewardship work focused on species at risk.
  • Private land owners have a very important role to play in species at risk recovery. If you find Rainbow Mussel in a watercourse on or adjacent to your property, you may be eligible for stewardship programs that support the protection and recovery of species at risk and their habitats.
  • You can help improve mussel habitat and keep Ontario’s water safe and clean by maintaining natural vegetation next to creeks and rivers. The roots of plants reduce erosion and can stop soil from washing into the river. Fence off streamside areas to keep cattle (and their manure) out of the water. There are many other things that you can do to help reduce soil erosion and you might be eligible for funding assistance. For more information, visit the Ontario Soil and Crop Improvement Association: www.ontariosoilcrop.org.

Did you know?

A mussel larva must attach to a host fish where it stays until is has consumed enough nutrients to transform into a juvenile mussel.

Did you know?

The female Rainbow Mussel goes fishing for host fish by producing a lure that looks just like a crayfish, including an eyespot and wriggling legs. When a fooled fish attacks the lure the mussel ejects its larvae, which have a better chance of attaching to the host fish at such a close distance.

Did you know?

Rainbow Mussel eggs hatch inside special pouches in the mother’s gills, called a marsupium. The larvae are supported in the marsupium through the winter until they are ejected into the host fish the following spring.

Did you know?

Mussels are indicators of environmental health. Since they have a complex life cycle, are long-lived (some species can live up to 100 years!) and eat by filtering water and its pollutants, mussels can provide a snapshot of how healthy our waterways are.

Did you know?

Aboriginal people harvested mussels for food and to create jewelry and tools. In the 1800s, massive numbers of mussels were harvested from the Grand River to create buttons. Millions were shipped out every year until the 1940s when plastic button became more popular.

The Endangered Species Act

Contact your local ministry office

Often the best source of local information on species at risk is your nearest ministry office. Call with your questions or concerns.