Above: Image © Emily Norton, iStockphoto.com

While daydreaming of your favourite summer swimming hole, you might remember seeing signs warning of health risks due to high levels of blue-green algae.

What is this bothersome bloom that has the potential to ruin a perfectly good day at the beach?

The scientific name for blue-green algae is cyanobacteria. Cyanobacteria are know as oxygenic phototrophs, which means they are organisms that derive their energy from photosynthesis and produce oxygen during the process. They are the oldest known type of these organisms, having been on the earth for more than 2.8 billion years.

Did you know? The name cyanobacteria is derived from the colour of the bacteria. The Greek word for blue is "kyanos".

The production of cyanobacteria during Earth’s early years is largely responsible for today’s oxygen-rich atmosphere and the evolution of higher forms of plants and animals. However, the production of cyanobacteria can sometimes become accelerated due to human-related activity (i.e., untreated sewage or runoff from agricultural sites containing fertilizers) or from natural causes.

Cyanobacteria primarily live in aquatic environments, which include salt water, fresh water and hot and cold springs. When these environments are exposed to increased nutrient levels, a process called eutrophication occurs, resulting in large blooms of cyanobacteria. The algae grow quickly under these conditions, but do not live long. This results in a large amount of decaying organic matter, which can wreak havoc on the ecosystem. The decay process consumes the oxygen dissolved in the water, which can result in the deaths of animals and plants relying on that oxygen to live.

Did you know? Eutrophication is caused by the addition of nutrients to an ecosystem, either naturally or artificially. Its name comes from the Greek words “eu” and “trope”, meaning “well” and “nourish”, respectively.

Blue-green algal blooms can also negatively impact humans. Many common cyanobacterial bloom species are capable of producing potent toxins that can cause serious health problems in humans and animals, such as liver, skin and digestive diseases, nerve damage and death. These blooms can also affect the taste of treated drinking water and recreational use of affected bodies of water decreases as a result of surface scums and unpleasant odours.

However, cyanobacteria do have some positive economic uses. Certain strains of the algae may be used as food or fodder, as they are high in vitamin and protein content. They are also sources for pharmaceutical products, such as antibiotics.

Even though some blue-green algae have positive attributes, it’s probably in your best interest this summer to avoid bodies of water with algae blooms because of the toxic properties mentioned above.

Learn More!

Health Canada website

Science Daily article


Graneli, E. and Turner, J.T., “Ecology of Harmful Algae (Ecological Studies)”, Springer, New York, 2007.




Miller, Frederic P., Vandome, A.F., and McBrewster, J., “Cyanobacteria” VDM Publishing House Ltd., Germany, 2009.

Paerl, H.W. and Huisman, J., “Climate change: a catalyst for global expansion of harmful cyanobacterial blooms”, Environmental Microbiology Reports, 2009, 1(1), 27-37

Article first published January 20, 2011.

Ricky Cheng

I am currently a fourth year undergraduate student in the honors physiology specialization program at the University of Western Ontario. I enjoy playing multiple sports which primarily include soccer and basketball.  I am applying for medical school this upcoming year.

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