Blue-Green Algae

Blue-green algae (BGA) are microscopic organisms found naturally in lakes and streams. They are usually found in low numbers but can rapidly increase in warm, shallow, surface water that receives a lot of sun. When this happens, they can form blooms that make the water look like green pea soup or turquoise paint. Some blue-green algae produce toxins that pose a health risk to people and animals.

When BGA is present in water, it is important to avoid drinking the water, using it for household purposes, or swimming in it. Keep pets away from the water as well, as there have been incidents in other jurisdictions where pets have died after drinking water containing blue-green algae.

If contact with a bloom does happen, wash with soap and water and rinse with clean water to remove the algae.

Testing for toxins can identify if the bloom is producing toxins at the time the sample was taken. However, a negative result does not mean that the bloom is not harmful. Blue-green algae can turn toxin production on and off in response to a complex suite of environmental factors. This means that toxins may be produced at different times during a bloom event.

The amount of time for a blue-green algal bloom and associated toxins to dissipate can vary drastically, depending on environmental conditions (e.g., temperature, sheltered area, winds, storm events, water depth, water flow). In general, the ministry recommends waiting approximately two weeks after a bloom is no longer visible before resuming normal use of lake waters.

BGA bloom in lakes in our region are rare BUT water temperatures are rising.


If You Suspect a BGA Bloom

If you spot a suspected blue-green algae bloom, report it to the Spills Action Centre at 1-800-268-6060.


Current Blue-Green Algae Notifications

Location Water Sample Date Date BGA Identified Toxin Analysis Date Toxin Analysis Posted
Surprise Lake September 16, 2020 September 24, 2020 TBD TBD
Madelaine Lake August 25, 2020 September 1, 2020 TBD TBD
Icarus Lake August 24, 2020 September 1, 2020 Indeterminate September 9, 2020
Warnica Lake August 13, 2020 August 26, 2020 No toxins detected September 21, 2020

Note that the toxin analysis is based on the sample taken on the original Water Sample Date. It does not necessarily represent the current condition of the lake. The toxin analysis typically takes approximately 5-7 business days from the date that blue-green algae is identified.

Note: For previous year blue-green algae notifications, visit Blue-Green Algae Historical Results



If you have questions, please contact the Thunder Bay District Health Unit at 807-625-5900 or toll-free at 1-888-294-6630 to speak with a public health inspector. The following links provide additional information.

Last Updated: 24/09/2020