Blue-green algae, also known as cyanobacteria, occur naturally in lakes and other bodies of water. Blue-green algae are not normally visible, but thrive in warm, shallow, slow-moving water, and can spread rapidly to form a large scum or bloom, most commonly in late summer and early fall. 

Blooms may make the water look bluish-green, or like green pea soup or turquoise paint. Fresh blooms often smell like newly mown grass, while older blooms may smell like rotting garbage.

Some varieties of this algae can produce toxins that are harmful to humans and animals and can cause diarrhea, vomiting, skin irritation and headaches. If you suspect a blue-green algae bloom, take a cautious approach and assume toxins are present. Avoid using, drinking, swimming, or bathing in the water, and restrict pet access.

There are simple, no-cost tests to check for blue-green algae. Filamentous green algae is commonly mistaken for blue-green algae blooms (it is not a a health hazard but can form dense, foul-smelling mats).  Pollen and duckweed are also mistaken for blue-green algae, although pine pollen slicks are more light yellow and occur in the Spring, and duckweed can be distinguished close up by its root structures.

Nutrient enrichment of surface waters by phosphorus and nitrogen can drive algal blooms. The MRC identified priority actions in response to episodes of blue-green algae in Gatineau Valley lakes, caused mainly by phosphorous:

• • make sure that septic facilities are up to standard

  • avoid spreading fertilizers close to lakes

  • ban the use of detergents with phosphates

  • maintain shorelines in their natural state

  • let lawns go so that nature can take over again

  • replant shorelines with appropriate shrubs.

See these links and documents below.

• Toxic blue green algae (Lac Notre- Dame and Usher Lake Association)

• Preventing health problems associated with blue-green algae

• Why is blue-green algae becoming more prominent?