Blue-green algae: What to do if you find it

Blue-green algae characteristics

Blue-green algae, or cyanobacteria, are bacteria that naturally occur in lakes and other waterbodies. They are not always harmful but can be in large quantities.

Here are some things to look for if you think you may have spotted a blue-green algae bloom:

Colour: often blueish-green or green like pea soup; can also be olive or reddish.
Smell: may smell fishy or have an odor like grass clippings, sewage, garbage or gasoline.
Consistency: like paint or soup; may appear scummy or foamy. Can form mats and blobs in large quantities.
Location: most likely to be in warm water with little current; may be more likely to occur in watersheds with development, agriculture and/or wetland loss upstream.
Time of year: most likely to appear in summer and early fall.

Other common species can be mistaken for blue-green algae. Click here to see some of them and compare with your sightings.

Common species that are mistaken for blue-green algae

Because blue-green algae (cyanobacteria) blooms don’t always look the same, other common species are sometimes mistaken for it. Here are few of the other species you may see in Canada’s lakes and waterbodies.

Duckweed vs. blue-green algae

Blue-green algae do not have roots or leaves. If you see this, it may be a tiny floating plant like duckweed.

Green algae vs. blue-green algae

If the substance appears to be silky or stringy, it may be a species of green algae. Blue-green algae are more likely to have a consistency like soup, scum or foam.

Tree pollen vs. blue-green algae

Yellowish film on the water, with a dusty texture, is likely to be tree pollen. You are more likely to see this in spring and early summer, whereas blue-green algae blooms are more likely to occur in summer and early fall, when the water temperatures are their warmest. Photo credit: Mary Holland

Chara algae. Photo Credit: Show_ryu, CC BY-SA 3.0, via Wikimedia Commons

Chara algae vs. blue-green algae

Also known as skunkweed or stonewart, these greenish algae have a plant-like appearance with branches and attach to sediment on the bottom—none of which are characteristics of blue-green algae.

Contact your provincial authority

If you think a nearby lake, beach or waterbody is suffering from a blue-green algae (cyanobacteria) outbreak, contact your provincial authority on lake and water health to report it.

British Columbia

Contact your regional B.C. health authority

Prince Edward Island

Contact the Department of Environment, Energy and Climate Action at 902-368-5044 or 1-800-565-1633

Alberta

Contact the Government of Alberta Environmental Hotline at 1-800-222-6514.

Nova Scotia

Contact your Department of Environment and Climate Change office or 1-877-936-8476

Saskatchewan

Contact Saskatchewan’s Healthy Beach Program

Newfoundland and Labrador

Contact Environment and Climate Change at water@gov.nl.ca or 1-709-729-2535

Northwest Territories

Contact Health and Social Services at 867-767-9052

Quebec

Contact 418-644-4545 (Québec area), 514-644-4545 (Montréal area), 1-877-644-4545 (elsewhere in Québec) or your regional office.

Nunavut

Contact your local Environmental Healthy region

New Brunswick

Contact your Department of Environment and Local Government regional office

What happens when your favourite lake gets sick?

Learn more about blue-green algae and the important role natural habitat plays in keeping our aquatic ecosystems healthy.

Learn more