What do dog deaths  in Fredericton, a State of Emergency  in Salem, Oregon, and vacuuming lakes  in Florida all have in common?

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All of these events over the past year have been triggered by microscopic organisms called cyanobacteria.

Knowing how to spot cyanobacteria in water can help you and your pets avoid serious health effects when swimming.

What Are Cyanobacteria?

"Cyanobacteria, also known as blue-green algae, are photosynthetic bacteria naturally present in surface waters in low or moderate numbers."

  • Cyanobacteria can occur as single cells or in groups, such as colonies (bunches) or filaments (long threads).

  • Buoyant cyanobacteria, such as anabaena and microcystis, may float upward when mixing is weak and accumulate in dense areas, which we call surface blooms.

Cyanobacterial bloom (left); Microcystis sp. (middle; magnified 200-fold); Anabaena sp. (right; magnified 400-fold)

Growth Factors

Environmental factors that cause the growth of cyanobacteria include:

  • High concentrations of phosphorus (> 25–50 µg total phosphorus per litre): fertilizers from farms are washed into lakes and streams.

  • High water temperature (> 25 °C): the ocean naturally absorbs heat but the build-up of greenhouse gases in the atmosphere increases the amount.

  • Temperature gradient: as lakes melt in the spring, water near the surface warms faster than deep water.

Cyanobacteria cells

Health Impacts

Breathing in or swallowing cyanobacteria can cause negative health effects in humans:

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  • headaches

  • drowsiness

  • loss of coordination

  • speech difficulties

Flaticon IconBody

  • fever

  • muscle aches & weakness

  • mouth blisters, skin rash, irritation in the eyes, nose & throat

Flaticon IconRespiratory

  • shortness of breath

  • dry cough

  • pneumonia

  • sore throat

Flaticon IconDigestive

  • abdominal pain & cramps

  • nausea

  • vomiting

  • diarrhea

Flaticon IconOrgans

  • kidney damage or disfunction

  • liver inflammation

Flaticon IconNervous System

  • sensations of tingling, burning, or numbness

Flaticon IconIt can also harm your pets — leading to liver failure, respiratory paralysis, or death — so keep an eye out for these symptoms:

  • coughing, shortness of breath, or other breathing difficulties

  • fatigue

  • convulsions

Health Impacts of Cyanotoxins.


You're walking with your dog along the lakeshore and you see blue-green algae on the water. What should you do?

Contact your local health authority

Go for a swim

Let your dog run in the water

Ignore it

Take Action

Help your local authorities spot cyanobacteria so they can treat it and keep your local water supply safe for swimming and drinking!

 Adam Sandler drinking a cup of water and saying,

If you see cyanobacteria on the surface of a body of water in your area:


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This Byte has been authored by


Raheema Afridi

Passionate for science, teaching and coffee.