Protecting fish and wildlife health

Diseases and parasites are a natural part of our ecosystems. Even if diseases and parasites are present, they may not have a significant effect on wildlife populations.

However, we monitor or control some fish and wildlife diseases if they impact:

  • fish and wildlife populations
  • human health

Keeping tabs on disease

The ministry runs programs to:

  • keep certain deadly wildlife diseases out of Ontario
  • minimize the impact of wildlife diseases

These programs include:

We also conduct research, monitoring and control programs to:

  • detect and identify emerging diseases
  • help prevent disease and parasites from spreading to new areas
  • protect public health
  • conserve the biodiversity of fish and wildlife species
  • address potential threats to Ontario’s economy

Learn more about our:

We also work closely with the Canadian Wildlife Health Cooperative (CWHC) to monitor Ontario’s wildlife health.

Fish and wildlife diseases

The following fish and wildlife disease are present or of concern in Ontario:

Fish and wildlife die-offs

From time to time, there are sudden or mass die-offs in fish and wildlife populations.

These deaths can be caused by:

  • diseases (for example, viral hemorrhagic septicemia (VHS))
  • toxins (for example, botulism)
  • low oxygen levels in water (fish)
  • stress from spawning or changing water temperatures (fish)

Learn how to report a fish or wildlife die-off.


Botulism sometimes causes fish and bird die-offs, with:

  • annual small-scale die-offs around the Great Lakes
  • infrequent large-scale die-offs

Type E botulism toxin is produced by a bacterium that naturally lives in lake-bottom sediment as harmless spores. The bacterium begins producing the toxin under certain conditions:

  • rich nutrient source (such as a dead animal)
  • complete lack of oxygen
  • optimum temperature

The toxin then enters the aquatic food chain, affecting fish and birds that eat molluscs or fish.

How to avoid botulism

Proper cooking and handling eliminates the botulism toxin. Make sure you:

  • cook all fish or waterfowl thoroughly
  • don’t consume sick or dying fish or waterfowl
  • don’t let pets eat the raw flesh of a contaminated bird or fish