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Blue-green algae blooms appeared earlier and on more lakes this summer than usual. Learn more about these blooms and the health risks they can pose.

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For information on Lakes in Wisconsin, contact:
Wisconsin DNR Lakes
Division of Water
Bureau of Watershed Management
Blue-Green Algae Contacts

Blue-Green Algae

Potential Effects on Humans and Animals

Can blue-green algae make me sick?

Yes, it is possible for blue-green algae to cause illness. Blue-green algae are capable of producing several different toxins. People may be exposed to these toxins through contact with the skin (e.g., when swimming), through inhalation (e.g., when motor boating or water skiing), or by swallowing contaminated water. Types of toxins and potential health effects include the following:

Dermatotoxins and Gastrointestinal Toxins These toxins affect the skin and mucous membranes, and can cause allergy-type reactions such as rashes, eye/nose/throat irritation, and asthma, as well as headaches, fever, and gastroenteritis (nausea, stomach cramps, vomiting, diarrhea). Examples include lyngbyatoxin and lipopolysaccharide endotoxins.

Hepatotoxins These toxins affect the liver and other internal organs, and can cause gastroenteritis, tissue damage, muscle weakness, paralysis, and respiratory failure (with acute exposure), tumors, and possibly liver cancer (with long-term, chronic exposure). Examples include microcystins and nodularins.

Cytotoxins These toxins also affect the liver and other organs (though through a different mode of action than hepatotoxins) and can cause malaise, headache, anorexia, vomiting, chromosome loss, DNA strand breakage, and damage to organs. An example is cylindrospermopsin.

Neurotoxins These toxins affect the central nervous system and can cause seizures, paralysis, respiratory failure or cardiac arrest. Examples include anatoxin-a and saxitoxin. (Saxitoxin is the same toxin associated with red tide and paralytic shellfish poisoning in marine systems).

Are children more vulnerable than adults?

Yes. Children may be at greater risk than adults for two primary reasons:

  1. Children 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.
  2. Children weigh less, and so a smaller quantity of toxin may trigger an adverse effect.

Can blue-green algae make my pet sick?

Animals are not necessarily more sensitive to blue-green algal toxins than humans. However, many animals, such as dogs and cattle, enjoy being in the water, even if there is an unsightly green scum layer floating on top. When such a bloom is present, 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 algal toxin poisoning may range from lethargy and loss of appetite to seizures, vomiting, and convulsions. Dogs are particularly susceptible to blue-green algal 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 containing algal blooms?

No. Animals can become extremely ill, and even die, after swallowing water containing blue-green algae. As public awareness has increased, so has the number of reports from veterinarians that blue-green algal toxins 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 blue-green algae is an underreported statistic.

Last Revised: Wednesday, July 24, 2013