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Blue-Green Algae: Get to Know its True Colours

Blue-green algae are naturally occurring and found in oceans as well as fresh water lakes, bays and inlets around the world. Unfortunately, reports of blue-green algae in Central Ontario waterways are becoming more common so it is important to know how blue-green algae can affect your health. Know the facts and reduce your risk.

Scientifically known as cyanobacteria, blue-green algae are microscopic organisms that have inhabited the earth for more than two billion years.

Normally blue-green algae are barely visible, but during warm weather the algae can rapidly increase to form a large mass called a bloom. Algae blooms usually occur in the hot summer months and early fall and tend to occur repeatedly in the same water bodies. Dense blue-green algae blooms can make the water look like a bluish-green pea soup, or a shiny paint slick. Fresh blue-green algae blooms often smell like fresh cut grass, while older blooms can stink like rotten garbage. Most algae blooms are short-lived and will break down in a few days or weeks.

While many forms of blue-green algae are harmless, some forms produce toxins that can be harmful to humans and animals. The risk depends on the type and amount of exposure to the toxins. Children are more vulnerable to the health effects of the toxins, but prolonged exposure to these toxins could also lead to long-term health problems for both adults and children.

To learn more about the three categories of blue-green algae, the different appearances and precautions, click on this chart.

For more information about blue-green algae, call the Health Unit toll-free at 1-866-888-4577.

Additional Resources:

Blue-Green Algae: Get to Know Its True Colours - HKPR

Video -HKPR District Health Unit

Fact Sheet - Blue-Green Algae - Ontario Ministry of the Environment

Fact Sheet - Blue-Green Algae: Information for Drinking Water System Owners and Operators - Ontario Ministry of Environment

Fact Sheet - Blue Green Algae: Background/Potential Impacts to Human Health and Safety of Drinking Water - Ontario Ministry of Environment

Health Canada

Blue Canoe Program


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