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Blue-Green Algae

Blue-green algae are tiny, plant-like organisms that occur naturally in ponds, rivers, lakes and streams. Blue-green algae blooms usually appear blue-green in colour but they can also be olive-green or red and will appear in large masses or as scum. Blooms usually appear in late summer and in the early fall especially in areas where the water shallow, slow moving and warm however blooms can also be found in deeper, cooler water. Blue-green algae will occur in waters that are rick in phosphorus and nitrogen usually caused by agricultural, storm water runoff as well as malfunctioning septic systems.

Blue-green algae can produce toxins that are harmful to both humans and animals. If you suspect a blue-green algal bloom:

  • assume toxins are present
  • avoid using, drinking, bathing or swimming in the water (call your local Health Unit for swimming advisories)
  • restrict pet and livestock access to the water

To report a blue-green algae bloom in Ontario please call the Ministry of Environment and Climate Change Spills Action Centre at 1-800-268-6060.

Information adapted from the Government of Ontario

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