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Utah APPLETREE Program


Health Information and Symptoms


Human Symptoms | Animal Symptoms | Exposure Routes | Background Info


Exposure to harmful algal blooms can cause a variety of health effects, from relatively mild to potentially serious. What symptoms people experience depends on many factors, including the amount of toxins/cyanobacteria, the type of toxin/cyanobacteria, the type of exposure, and the length of exposure.

No human deaths in the United States have been caused by cyanotoxins; however, pet, livestock, and wildlife deaths caused by cyanotoxins have been reported throughout the United States and the world (CDC, 2016).


Human Symptoms

Swallowing water

  • Vomiting
  • Diarrhea
  • Stomach pain
  • Weakness
  • Headache
  • Tingling sensation
  • Muscle cramps
  • Dizziness
  • Trouble breathing

Skin contact with water

  • Eye irritation
  • Rash
  • Hives
  • Blisters or sores

Breathing droplets of water

  • Nose irritation
  • Sore throat
  • Coughing or wheezing
  • Asthma-like symptoms
  • Respiratory symptoms (including difficult, rapid, or shallow breathing)


Pet and Animal Symptoms

  • Weakness
  • Fatigue
  • Excessive saliva production or drooling
  • Staggering
  • Difficulty breathing
  • Vomiting
  • Convulsions


Background Information | Top

When present in high numbers in recreational waters, blue-green algae can cause eye, ear, and skin irritation. Gastrointestinal symptoms such as vomiting and diarrhea can also result from exposures to blue-green algae. Animals such as dogs and cattle may become sick from eating the blue-green algae surface scum.

Most types of blue-green algae have the ability to produce toxins that can be classified into two major types: hepatotoxins and neurotoxins. Hepatotoxins affect the liver; blue-green algae hepatotoxins include microcystin, nodularin, and cylindrospermopsin. These toxins are commonly produced by the Microcystis, Nodularia, and Cylindrospermopsis species, respectively. These toxins cause symptoms such as nausea, vomiting, and acute liver failure. In general, symptoms will appear rapidly following exposure to high amounts of hepatotoxins, but may take several days in the case of more moderate exposure.

Neurotoxins affect the nervous system; blue-green algae neurotoxins include anatoxin-a, anatoxin-a(s), and saxitoxin. These are commonly produced by the Anabaena and Oscillatoria species. Animals or humans ingesting these toxins may develop muscle cramps, twitching, paralysis, and cardiac or respiratory failure. Symptoms can occur within an hour of exposure, but may take as long as 36 hours to develop.

Though the most serious health effects of harmful algal blooms are due to the toxins, skin irritation and rashes may also result from contact with blue-green algae even in the absence of toxins. Like many types of bacteria, the outer layers of the cells themselves can have compounds that cause these symptoms.