Toxic Blue-Green Algae

toxic blue-green algaeBlue-green algae are a type of bacteria called cyanobacteria, which produce toxins called cyanotoxins. Exposure to water that contains these toxins is dangerous and potentially deadly to several species, including humans and their pets.

Blue-green algae live in non-running, freshwater ecosystems such as lakes and ponds, and grow in colonies called “blooms” that give water a blue-green appearance. Colonies of toxic blue-green algae are sometimes called harmful algal blooms (HABs). Not all blue-green algae are toxic blue-green algae; however, because the only way to determine the safety of algae is to test it, the Pet Poison Helpline recommends considering all algae blooms as potentially dangerous.

Where Blue-Green Algae Occurs

Blue-green algae are present throughout North America. According to the American Society for the Prevention of Cruelty to Animals (ASPCA), these blooms “thrive in bodies of fresh water when the weather is warm (over 75 degrees) and sunny.” Lynn Buzhardt, DVM elaborates that algae “grow readily in hot, humid climates where water is warm. Although the largest algae bloom occurs in late summer and early fall, it has a longer growing season in temperate climates.”

Animals Are Affected by Toxic Blue-Green Algae

As Miranda Carney writes in an article for the American Kennel Club, dogs are generally viewed as being at higher risk because they are more likely to play in or drink from non-flowing freshwater. However, other animals including pasture animals (for example, cows, horses, or sheep) are also at risk: “Livestock that drink stagnant water from troughs may also ingest toxic algae,” says Dr. Buzhardt. She also notes that, while cats are also susceptible to cyanobacteria, they are at lower risk because “they rarely swim and are pretty picky about the water they drink.”

Symptoms of Toxic Exposure to Cyanobacteria

As Kendall Curley explains in the article How to Protect Your Pet from Toxic Blue-Green Algae, several cyanobacteria produce toxins that “affect different parts of the body.” Symptoms of exposure vary according to the particular type of toxin:

Dermatologic (Skin)

Bluish tint

Pale gums

Hepatotoxins (Liver)



Blood in the stool or black, tarry stool

Pale mucous membranes


Neurotoxins (Brain)

Weakness and/or disorientation

Muscle twitches or tremors

Excessive drooling, tearing, urination, and defecation

Difficulty breathing


Heart failure


Prevention Is Crucial for Pet Safety

Prevention is the best method for keeping your pet safe from the serious effects of toxic blue-green algae. According to the United States Environmental Protection Agency (EPA), do not allow your pet to enter or drink water if:

  • The water is slimy, looks like foam, scum, or mats floating on the water.
  • If there is a bluish-green scum accumulated around the edges of the body of water. The Pet Poison Helpline notes that cyanobacteria float and “may be blown by the wind into thick, concentrated mats near the shore,” making it accessible to animals and people even if they aren’t in the water.
  • The water is discolored. According to the EPA, HABs “can be blue, bright green, brown or red and may look like paint floating on the water.”
  • The water has a foul or pungent smell. “Some (but not all) harmful algae produce a nauseating smell,” says the EPA

What to Do if Your Pet is Exposed

There are currently no antidotes for toxic blue-green algae, and so exposure may be incredibly dangerous. “Very small exposures, such a few mouthfuls of algae-contaminated water, may result in fatal poisoning,” warns the Pet Poison Helpline. Blue-green algae are also dangerous because their toxicity takes effect so quickly; “signs of poisoning occur within 30-60 minutes of exposure,” says Dr. Buzhardt.

Take action immediately if you think your pet has been exposed:

  • The ASPCA explains that algae cells “can also stick to a pet’s fur and be ingested when they clean themselves,” so do not allow them to lick their fur, and immediately wash them off using clean water.
  • If the water has been ingested, rush to the nearest veterinarian. Curley states that, in some cases, a veterinarian may be able to induce vomiting “and/or give medications like activated charcoal or cholestyramine to prevent absorption of more toxin.”
  • Further care may be required to completely rid the toxin from the system. Treatments vary according to the type of toxin, as well as the severity of symptoms, and must be assessed by a veterinarian depending on the animal’s individual needs.

Report any water source to your state’s health department if you suspect it is contaminated. “By reporting these instances,” writes Curley, “you can not only help prevent other people and pets from exposure, but you can also help researchers to understand, track and prevent these blooms.”

Written by Laura Strommen

Edited by the Staff at Pet Health

© Pet Health, a division of Women’s International Pharmacy, Inc.