Living with Us… Blue-Green Algae

Blue-green algae, also known as cyanobacteria (“sigh-ano-bacteria”), are a type of plant-like bacteria that are very small and under normal conditions, can only be seen under a microscope. These bacteria are naturally present in our freshwater lakes and streams in low numbers, but can rapidly increase in population in warm, shallow, undisturbed surface water that gets a lot of sun. This is called a “bloom”.

Other factors that contribute to blue-green algal blooms are an increase of nutrients (eutrophication). Eutrophication leads to a bloom by providing the algae with unlimited nitrogen and phosphorous, which are nutrients essential for their growth. 

Blooms most commonly occur in late summer and early fall and are usually identified by a floating mass or scum on the surface of the water that is blue green in colour. When the blooms start to die off, their cells produce a toxin, known as a cyanotoxin or liver toxin, that is harmful, and even lethal to humans and animals if ingested.

Not only are they a threat to living beings, they can cause a reduction in water quality. This is done by the algae limiting the amount of sunlight in the water, resulting in the death of underwater plants. For fish, the toxins produced by blue-green algae can affect the development of fish eggs and can also accumulate in the organs of fish.

Did you know… A fresh algae bloom often smells like newly mowed grass, while older blooms may smell like rotting garbage. Also, not all algae are toxic algae. There are “true” algae (or green algae) which are a source of food for aquatic organisms, where cyanobacteria are not. Despite there being safe algae and toxic algae, when a bloom is present one should always use caution and assume that toxins are present and avoid using the water where the bloom was found. If you would like more information on this and other Four Rivers initiatives, please contact [email protected]

Cover Image: Group of multiple individuals of Gliotrichia species, a type of cyanobacteria. Viewed at 100x magnification

Individuals of Lyngbya species, a type of cyanobacteria. Viewed at 200x magnification.