Blue-Green Algae or Cyanobacteria


We wish to remind residents to stay out of beach/river water if it appears bright green or pea soup in colour.

Blue-green algae are microscopic plants that live in fresh water and their scientific name is Cyanobacteria. Normally blue-green algae are barely visible, but, during warm weather, populations can rapidly increase to form a large mass called a bloom. Blooms most commonly occur during the late summer and early fall. Blue-green algae blooms are natural phenomena that occur in fresh water around the world. Blooms of Cyanobacteria have been reported in various locations throughout Ontario where they are a seasonal phenomenon and tend to occur repeatedly in the same water bodies. The growth rates of blue green algae are directly affected by levels of phosphorus and nitrogen in surface waters. Human activities contribute to the increase in phosphorus and nitrogen in our waters through activities such as agricultural runoff, household fertilizer runoff, faulty septic systems, and  improper waste management systems.

How can I recognize a blue-green algae bloom?

  • Dense blue-green algae blooms may make the water look like bluish-green pea soup.
  • When the bloom is very large, algae may form solid looking clumps.
  • Fresh blooms often smell like freshly cut grass; older blooms smell like rotting garbage.

What are the potential health effects associated with blue-green algae toxins?

  • Itchy, irritated eyes and skin that may result from direct contact such as swimming.
  • If the toxins are swallowed, symptoms such as headaches, fever, diarrhea, abdominal pain, nausea, and vomiting are possible. Higher levels of risk to human health are linked to ingestion of large quantities of Cyanobacteria toxins in water. Usually people won’t drink water contaminated with blue-green algae blooms because of its unsightly pea soup appearance and foul smell.

How do I protect myself?

  • Avoid activities that increase the chance of exposure to these algae blooms
  • Do not drink, bathe, or shower in untreated surface water.
  • Do not allow children, pets and livestock to drink or swim in the water.
  • Do not boil the water. Boiling may release more toxins into the water.
  • Be cautious about eating fish caught where blue-green algae blooms occur; Do not eat the liver, kidneys and other organs.
  • Do not treat the water with a disinfectant like chlorine (bleach). This may break open algae cells and release toxins into the water.

How does the Chatham-Kent water treatment plant deal with Cyanobacteria?

  • The Chatham-Kent municipal water treatment plant regularly tests for Cyanobacteria toxins in the water supply. To date they have not detected any of these toxins in our water supply.
  • If Cyanobacteria are detected in the water supply, treatment plants can remove them in a number of ways.

For more information on Cyanobacteria check out the Ontario and Health Canada websites.


About Author


  1. Hi,

    I lead the group at NOAA who monitors algal blooms in Lake Erie,
    including satellite data.
    We will try to support you on the problem along your shore, and also
    get more information.
    I’d like to connect with appropriate people. Thank you.

    –Rick Stumpf