Blue-Green Algae Bloom

Picture of blue-green algae bloomBackground

Cyanobacteria, commonly known as “blue-green algae”, are not true algae but are a type of photosynthetic bacteria found in some freshwater bodies throughout the world.  Under certain conditions, the cyanobacteria accumulate within the water and can form a “bloom” or a blue-green “scum” on the water’s surface. In addition to the nuisance (fouling) and aesthetic (odour) problems caused by blue-green algae blooms, several species of cyanobacteria have the ability to create toxins that can be harmful to humans and animals. Factors that contribute to harmful algal blooms are complex but can include an increase in nutrient inputs and human activities. An increase in surface water temperatures related to climate change has also been shown to increase bloom events.

Watch this video from Environment Ontario: What causes blue-green algae blooms?

Toxic blue-green algae – what is it, and what causes it to bloom? We asked our scientists – watch to find out


Reporting and Notification

Water samples can be taken by the Ministry of Environment’s Operations Division staff responding to reports of blue-green algae blooms to confirm the presence of any toxin. 

Timiskaming Health Unit will notify the public if there is a risk to public health. The public should avoid swimming, bathing, drinking the water, and allowing pets into the water if the algae bloom is present. If no bloom is present, water can be used for regular recreational activities. 

If you spot blue-green algae blooms, call the Spills Action Centre
1-866-MOETIPS (6638477)
TTY: 1-855-889-5775

If cyanobacter blooms are present or reported, the public should:

  • Avoid using the lake water for drinking, bathing, swimming or showering and do not allow children, pets or livestock to drink or swim in the lake water. 
  • Not boil the water because boiling the water may release more toxins into the water. 
  • Avoid cooking with the water because food may absorb toxins from the water during cooking. 
  • Exercise caution with respect to eating fish caught in water where blue-green algae blooms occur. 
  • Not treat the water with a disinfectant like bleach. This may break open algae cells and release toxins into the water.
  • Not rely on water jug filtration systems because they do not protect against the toxins

What are the potential health effects from drinking or coming in contact with water containing blue-green algae?

Some blue-green algae produce toxins that can pose a health risk to people and animals when they are exposed to them in large enough quantities. Health effects can occur when surface scum or water containing high levels of blue-green algal toxins are swallowed, through contact with the skin, or when airborne droplets containing toxins are inhaled while swimming, bathing or showering.

Consuming water containing high levels of blue-green algal toxins has been associated with effects on the liver and on the nervous system in laboratory animals, pets, livestock and people. Livestock and pet deaths have occurred when animals consumed very large amounts of accumulated algal scum from along shorelines.

Direct contact, or breathing airborne droplets containing high levels of blue-green algal toxins during swimming or showering, can cause irritation of the skin, eyes, nose and throat and inflammation of the respiratory tract.

Recreational contact, such as swimming, and household contact, such as bathing or showering, with water not visibly affected by a blue-green algae bloom is not expected to cause health effects. However, some individuals can be especially sensitive to even low levels of algal toxins and might experience mild symptoms such as skin, eye or throat irritation or allergic reactions.

Harmful Algae Blooms Know the Facts - Reduce Your Risk  (PDF)

Information for drinking water system owners and operator (PDF) 

For more information about blue green algae, visit (

Waterways affected by blue-green algae

Municipality Date of Sampling Additional comments
 Lake Kenogami Eby Township  2023-08-15 Bloom observed and microcystin toxins present. 
 Larder Lake McFadden Township  2023-08-10  Bloom observed and microcystin toxins present.
Lake Temiskaming Temiskaming Shores  2023-08-01  Bloom observed and microcystin and dolichospermum present. 
Round Lake  Marquis Township  2023-07-04  Bloom observed and microcystin toxins present. 
Lake Temiskaming Temiskmaing Shores  2022-08-24  Bloom observed, and toxins present.
Larder Lake (near Island U) Township of Larder Lake 2022-07-04 Bloom observed.
Toxin below detection limits.
Lost Lake
2021-10-06  Bloom observed.
Kenogami Lake Kenogami 2021-10-08  Bloom observed.
Fairy Lake Township of Hudson 2021-07-17 

Bloom observed. Toxins below detection limits. 

Lake Temiskaming Temiskaming Shores 2021-06-28  Bloom observed and microcystin LR toxins present. 

Sampling is conducted by the MOE