Fish Die-offs: Frequently Asked Questions

What causes a fish die-off?

  • Seasonal Stressors: Fish die-offs commonly happen in spring and summer, often related to spawning stress, rapid temperature changes, or disease.
  • Winter Kill: In cold, prolonged winters, thick ice cover prevents oxygen from recharging in the water, sometimes causing fish to die. These die-offs may only become visible in early spring as the ice melts.
  • Oxygen Depletion: Weather, water quality, temperature, and algae growth can lead to reduced oxygen in the water, causing fish to suffocate鈥攐ften in shallow lakes with abundant plant growth.
    • Aquatic plants produce oxygen during the day but use it at night.
    • Long periods of calm, hot weather reduce the recharging effect of waves, so less oxygen is introduced into the water.

What should I do if I see a fish die-off?

  1. Report It
    • Ministry of Natural Resources (MNR) Fish Die-Off Hotline: 1-800-387-7011
    • If you suspect a spill or contamination event, call the Ministry of Environment, Conservation, and Parks (MECP) Spills Action Centre: 1-800-268-6060
    • It is important that the MNR and MECP are contacted first. If time allows, UTRCA staff also appreciate receiving the information and can be contacted through our online form.
  2. Check Nearby Conditions
    • Look for obvious signs of pollution (unusual coloration, strong chemical smells) or extensive algae blooms.
    • If the fish kill is large or the circumstances seem unusual, authorities can investigate.

Are birds and other wildlife safe around a fish die-off?

  • Naturally Occurring Fish Kills
    • If fish die from oxygen depletion (commonly called 鈥渟ummer kill鈥� or 鈥渨inter kill鈥�), scavengers like turkey vultures, gulls, crows, turtles, raccoons, and coyotes will typically eat the fish without serious harm.
    • In a natural system, these carcasses decompose or are eaten, returning nutrients to the ecosystem.
  • Contamination Concerns
    • If chemical spills or toxic algal blooms caused the die-off, then anything eating those fish could be at risk. This is why it鈥檚 important to contact MNR or MECP if you suspect contamination.
  • Pets (Especially Off-leash Dogs)
    • Dogs can be attracted to rotting fish and may become sick if they eat or roll in it. They have less tolerance for decaying meat or potential toxins compared to specialized wildlife scavengers.
  • Will Wildlife Scavengers 鈥淐lean Up鈥� Quickly?
    • Often, wild scavengers (vultures, raccoons, coyotes, turtles) can remove carcasses within a few days.
    • Larger or more widespread kills may linger longer, especially in areas with fewer scavengers.

Should I clean up the fish?

  • Individual Landowners
    • If dead fish wash up on the shore, landowners are typically responsible for cleanup on their property.
  • Municipalities
    • Municipalities are responsible for public beaches and other municipal properties.
  • Provincial Parks
    • MECP is responsible for removing dead fish from swimming beaches in Provincial Parks.
  • Natural Decomposition
    • MNR does not collect dead fish floating in lakes or private waters. Typically, the dead fish will sink and decompose or be eaten by scavengers.

Should I post signs?

  • When to Post Signs
    • If a fish die-off occurs near well-used trails, beaches, or dog-walking areas, posting a temporary sign can help prevent off-leash dogs (or curious people) from touching or eating the fish.
    • The sign might warn owners that dead fish are present and can pose a health risk to pets.

Practical Tips if You Find a Dead Fish:

  1. Assess the Situation
    • One or two fish on your shoreline? Likely a natural occurrence.
    • Large numbers of fish? Contact the fish die-off hotline (1-800-387-7011).
  2. Letting Nature Take Its Course
    • In a remote, natural area: leaving a few dead fish is usually fine鈥攖hey feed scavengers and recycle nutrients.

Key Takeaways:

  • Fish kills happen regularly from natural factors (especially oxygen depletion) and are often not a major threat to wildlife or humans.
  • Always report unusual or large die-offs to the MNR hotline (1-800-387-7011). If you suspect spills or toxins, call MECP (1-800-268-6060).
  • Scavengers (birds, turtles, raccoons, coyotes) usually handle naturally killed fish without harm, but pets might be at risk if they ingest rotting or contaminated fish.
  • Landowners are responsible for disposal on their own property. Municipalities handle public land.
  • Signs may help alert pet owners if there is a significant die-off in a popular area.
  • For more detailed guidance, visit the Ontario government or consult local bylaws.

By following these guidelines鈥攁nd calling the appropriate hotlines when needed鈥攜ou can ensure both public safety and environmental stewardship.

Fish die-off

Fish die-off