Cover photo credit: Karen Little, Illinois State Museum


Special Concern

“Special Concern” means the species lives in the wild in Ontario, is not endangered or threatened, but may become threatened or endangered due to a combination of biological characteristics and identified threats.

Date added to the Species at Risk in Ontario List

Rainbow was already assessed as threatened when the Endangered Species Act took effect in 2008. It was reassessed as special concern in June of 2016.

Read the assessment report

What it looks like

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.

Where it lives

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.

Where it’s been found in Ontario

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.

What threatens it

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.

Action we are taking

Special concern species do not receive species or habitat protection, but may be eligible for grants to help with their protection and recovery.

What you can do

Report a sighting

Report a sighting of an endangered animal or plant to the Natural Heritage Information Centre. Photographs with specific locations or mapping coordinates are always helpful.


Volunteer with your local nature club or provincial park to participate in surveys or stewardship work focused on species at risk.

Be a good steward

  • private land owners have a very important role to play in species recovery; if you find a nesting on your land, you may be eligible for stewardship programs that support the protection and recovery of species at risk and their habitats
  • 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:
  • 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 website

Report illegal activity

Report any illegal activity related to plants and wildlife to 1-877-TIP-SMNR (847-7667).

Quick facts

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