Health Effects of Harmful Algal Blooms

Harmful algal blooms contain cyanobacteria that can cause skin irritation, gastrointestinal illnesses, and in some cases, produce toxins that cause serious health impacts to people, livestock, and pets.

You can be exposed to the harmful effects of cyanobacteria by:

  • Getting them on your skin while swimming or wading
  • Inhaling airborne toxins when boating, or jet-skiing, or water skiing
  • Drinking contaminated water

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

In the event you do come into contact with water contaminated with cyanotoxins, rinse off with clean, fresh water as soon as possible. Remove yourself from the source of exposure and contact the Utah Poison Control Center at 800-222-1222.


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


Pets are more sensitive to cyanotoxins (9 MB) 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.


Skin contact

People or animals exposed through direct skin contact or inhalation may experience the following symptoms:

  • Skin irritation
  • Eye irritation
  • Nose irritation
  • Throat irritation
  • Respiratory irritation


People who ingest cyanotoxins may experience the following symptoms:

  • Abdominal pain
  • Headache
  • Neurological symptoms
  • Vomiting
  • Diarrhea
  • Liver damage
  • Kidney damage


Toxigenic cyanobacteria — the type of cyanobacteria that can produce toxins — are responsible for four main types of toxins.


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).


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.


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.


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

CyanotoxinAcute Health Effects in HumansMost Common Cyanobacteria Producing These Toxins
Microcystin-LRAbdominal pain, headache, sore throat, vomiting and nausea, dry cough, diarrhea, blistering around the mouth, and pneumoniaMicrocystis, Anabaena, Nodularia, Planktothrix, Fischerella, Nostoc, Oscillatoria, and Gloeotrichia
CylindrospermopsinFever, headache, vomiting, bloody diarrhea, liver inflammation, and kidney damageCylindrospermopsis 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 groupTingling, 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

References & More Info