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Harmful Algal Blooms: Health Effects

Can cyanobacteria make me sick?

Yes. Cyanobacteria are capable of producing several different types of toxins. You can be exposed to these toxins by:

  • Getting it on your skin while swimming or wading
  • Inhaling airborne toxins when motor-boating or waterskiing
  • Drinking contaminated water

Exposure to cyanotoxins can cause a range of health effects, from a mild skin rash to serious illness or death.

What kinds of toxins are produced by cyanobacteria?

Cyanobacteria produce four main types of toxins.

Dermatoxins

These toxins affect the skin and mucous membranes. Symptoms range from allergic–like reactions such as a runny nose, sore throat, or asthma to flu–like reactions, skin rashes, nausea, or vomiting. Examples include dermal toxins produced by Lyngbya (lyngbatoxin).

Hepatotoxins 

These toxins affect the liver and other internal organs, and can cause nausea, vomiting, muscle weakness, and acute liver failure. Examples include microcystin, cylindrospermopsin, and nodularin.

Cytotoxins 

These toxins also affect the liver and other organs, though through a different mode of action than hepatotoxins, and can cause headache, vomiting, and damage to organs. Examples include cylindrospermopsin,

Neurotoxins

These toxins affect the central nervous system and can cause seizures, paralysis, respiratory failure, or cardiac arrest. Examples include anatoxin-a, anatoxin-a(s), and saxitoxin. Anatoxin-a is a potent neurotoxin that can cause death within minutes or hours, which is why it was originally known as Very Fast Death Factor (VFDF). Anatoxin degrades quickly, with a half-life of less than 24 hours in most natural blooms. This rapid degradation creates problems for determining toxin levels after exposure. 

The Primary Cyanotoxins and Their Health Effects

Cyanotoxin

Acute Health Effects in Humans

Most Common Cyanobacteria Producing Toxin

 Microcystin-LR

Abdominal pain, headache, sore throat, vomiting and nausea, dry cough, diarrhea, blistering around the mouth, and pneumonia

MicrocystisAnabaenaNodulariaPlanktothrixFischerellaNostoc, Oscillatoria, and Gloeotrichia

 Cylindrospermopsin

Fever, headache, vomiting, bloody diarrhea, liver inflammation, and kidney damage

Cylindrospermopsis raciborskii, Aphanizomenon flos-aquae, Aphanizomenon gracile, Aphanizomenon ovalisporum, Umezakia natans, Anabaena bergii, Anabaena lapponica, Anabaena planctonica, Lyngbya wollei, Rhaphidiopsis curvata, and Rhaphidiopsis mediterranea

 Anatoxin-a group

Tingling, burning, numbness, drowsiness, incoherent speech, salivation, respiratory paralysis leading to death*

Chrysosporum (Aphanizomenon) ovalisporum, Cuspidothrix, Cylindrospermopsis, Cylindrospermum, Dolichospermum, Microcystis, Oscillatoria, Planktothrix, Phormidium, Anabaena flos-aquae, A. lemmermannii Raphidiopsis mediterranea (strain of Cylindrospermopsis raciborskii), Tychonema and Woronichinia

* Symptoms observed in animals.

Are children more vulnerable than adults?

Yes. Children may be at greater risk than adults. They love to play in the water, but typically do not understand the health risks as well as adults. As a result, they may drink the water because they are thirsty or swallow it accidentally while swimming. In addition, children weigh less, and so a smaller quantity of toxin may trigger an adverse effect.

Can cyanobacteria make my pet sick?

Pets are more sensitive to cyanotoxins than humans. When a bloom is present, animals may consume large quantities of cyanobacteria if they drink the water, and if those cyanobacteria happen to be producing toxins, the animals can become very ill and even die. Symptoms of cyanotoxin poisoning may range from lethargy and loss of appetite to seizures, vomiting, and convulsions. Dogs are particularly susceptible to cyanotoxin poisoning because scums can attach to their coats and be swallowed during self-cleaning.

Should I let my pets or livestock drink or swim in water experiencing algal blooms?

No. Animals can become extremely ill, and even die, after swallowing water containing cyanobacteria. As public awareness has increased, so has the number of reports from veterinarians that cyanotoxins may have played a role in the deaths of dogs where other causes were not obvious. It is possible that the number of dogs that die from exposure to cyanobacteria is an underreported statistic.

How do you treat people that have been exposed to cyanotoxins?

In the event that you do come into contact with water that is known to be contaminated with cyanotoxins, the Centers for Disease Control (CDC) recommends that you rinse off with clean, fresh water as soon as possible. Remove yourself from the source of exposure and get supportive treatment. Seek medical treatment right away if you think you or someone you know might have been poisoned by cyanobacterial toxins, especially if you recognize any of the symptoms mentioned above. For more information, please visit the CDC's webpage on Harmful Algal Blooms (HABs).

References and More Information