Municipal Affairs and Environment

Blue-Green Algae: Frequently Asked Questions

Effects of Toxins on Humans and Animals

  1. How can blue-green algae toxins affect people?
  2. Can blue-green algae toxins harm me?
  3. How can blue-green algae toxins affect animals?

1. How can blue-green algae toxins affect people?

Humans are susceptible to blue-green algae toxins, but most people avoid drinking affected water because of the objectionable appearance and odour of a blue-green algae bloom. This explains the few records of toxicity causing death in humans. The accidental ingestion of blue-green algae during swimming and water skiing can result in fever, headache, dizziness, stomach cramps, vomiting, diarrhea and sore throat. Humans can also suffer skin and eye irritation and swelling, and swollen lips. These symptoms seldom persist for more than two or three days. Children can be more intensely affected because they may spend more time in the water than adults and have lower tolerance to the toxins.

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2. Can blue-green algae toxins harm me?

Although many people globally have become ill from exposure to blue-green algae toxins, poisoning from contaminated drinking water is unlikely to occur given that drinking water supplies are usually effectively managed to control taste, odour and other problems. It is possible that extended exposure to low levels of blue-green algae hepatotoxins can have long-term or chronic effects in humans.

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3. How can blue-green algae toxins affect animals?

Though not necessarily more sensitive to blue-green algae toxins than humans, many animals, such as dogs and cattle, may enter and ingest water even if there is an obvious bloom occurring. During a bloom, animals may consume large quantities of blue-green algae if they drink the water, and if those blue-green algae happen to be producing toxin(s), the animals can become very ill, and even die. Symptoms of blue-green algae toxin poisoning may range from lethargy and loss of appetite to seizures, vomiting, and convulsions. Dogs are particularly susceptible to blue-green algae poisoning because the algae can attach to their coats and be swallowed during self-cleaning. If a bloom is visible, do not allow livestock or pets access to the affected water and provide alternative sources of drinking water.

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