Cyanobacteria (also referred to as blue-green algae) is a type of bacteria found in many lakes, ponds, and reservoirs. Cyanobacteria can multiply a lot in the summer, causing extensive growths called blooms. The blooms cause scum on the surface of water and can be blue-green or greenish-brown and often smell musty or grassy.

Some bloom-forming types of cyanobacteria produce toxins. When toxic blooms die and decay, toxic chemicals may be released into the water. Some toxins can be in the water at low levels for many months after a bloom forms. Some blooms are so bad that they cause livestock deaths. Some blooms don’t contain toxins, but you can’t tell if a bloom is harmful or not from how it looks. If you see a bloom, always take precautions as if it is toxic.

How does cyanobacteria affect human health?
Children might be more at risk for getting sick from cyanobacteria because they often spend more time in the water and may swallow contaminated water by accident.

If you have contact (e.g., swimming, boating) with water containing cyanobacteria, you may experience:
• skin irritation and rash
• sore throat
• sore, red eyes
• swelling of the lips
• hay fever symptoms (e.g., stuffy nose)

If you drink water containing cyanobacteria, you may experience:
• headache
• diarrhea
• weakness
• liver damage
• fever (temperature more than 38.5 °C or 101.3 °F)
• nausea and vomiting
• muscle and joint pain
• stomach cramps

Treat all cyanobacteria blooms with caution. Call Health Link at 811 if you have been in contact with water that has a cyanobacteria bloom and are having symptoms.

How does cyanobacteria affect livestock and pets?
Lakes contaminated with cyanobacteria can be deadly if toxins are present. Some illnesses and deaths of livestock and wildlife have been linked to animals drinking water containing cyanobacteria. Keep animals away from natural water sources that contain cyanobacteria blooms because animals aren’t concerned about how water looks or smells before they drink it. Don’t let animals eat whole fish or trimmings (any waste from filleting a fish including the head, bones, intestines, or skin) from affected lakes.

What about watering my vegetable garden?
Don’t use water with cyanobacteria to water edible plants (especially plants with edible parts exposed to the ground surface, such as cabbage, lettuce, tomatoes, and other salad vegetables). It is not known if fruits and vegetables absorb toxins from contaminated water.

Is it safe to cook with water that might contain cyanobacteria?
Boiling water doesn’t remove cyanobacteria toxins. Don’t cook with water that might contain cyanobacteria.

What else do I need to think about?
• Treat any cyanobacteria bloom as if it is contaminated.
• Don’t swim or wade in water with scum on the surface.
• Don’t drink water if it might be contaminated with cyanobacteria.
• Have another source of drinking water for pets and livestock.
• If you see a bloom or have questions about cyanobacteria, call Environmental Public Health 1-833-476-4743.
• Call Health Link at 811 if you have been in contact with contaminated water and have any of the symptoms listed above.
• Call a vet if your pet has been in contact with contaminated water.