The Dangers of Blue Green Algae

Blue-Green Algae Toxicity

It is every dog owner’s worst nightmare- you take your dog out for a fun day in the water and before the day is through your best friend is in a fight for their life.

In recent weeks, stories like this have become more common on the news and social media.  Dogs spend a day playing in the water and, soon after, they start displaying a terrifying set of symptoms. It is not uncommon for these dogs to not survive the ordeal despite emergency veterinary care.  The source of these horror stories? Blue-Green algae growing in our lakes, streams, and other bodies of water; and it is becoming more common.

The source of these terrifying toxicities are not actually the algae, it is a toxin called microcystin produced by certain species of cyanobacteria, also known as blue-green algae.  Incidents have been most common in the Southeast, but the toxin can be found all over the United States as weather becomes warmer and rain becomes more scarce. 

Blue-green algae usually flourishes in lakes and other quiet bodies of water, but it can also be found in streams, bodies of salt water, backyard fountains, damp soil, and even on rocks.  It most commonly looks like a bluish-green “scum,” or foam at the edge of the water.  It may also appear reddish brown, pea green or neon green, or may look like paint or motor oil floating on the surface of the water.

Photo of Blue Green Algae from CDC Website

(original image:

While cyanobacteria toxicity can also affect humans, it is much more common in dogs as they are more likely to ingest water while they swim and play.  The algae can also stick to a dog’s fur, which they may later lick off.  Signs of toxicity can show up 15 minutes to several days after ingestion and include symptoms associated with liver or neurologic toxins:

Cyanobacteria toxicity can be fast and severe, so prevention is key.  Do not allow your dog to play in water if you have any reason to believe algae may be present.  If you do allow your dog to spend time in the water, please follow these precautions:

    • Check with available local and state agencies that monitor water quality to look for reports of algae blooms or other dangerous contaminants
    • Stay away from stagnant ponds or bodies of water, as they are more likely to contain blue-green algae
    • Discourage your pet from interacting with backyard ponds, fountains, bird baths, etc.
    • Encourage your dog to drink plenty of fresh water, so they are less likely to drink from the water they are playing in
    • Wash or rinse your dog well after playing in water, as algae can stick to fur

For more information on blue-green algae or other Harmful Algae Blooms (HABs), visit the CDC website:


In San Diego County, the following websites monitor water quality and report Harmful Algae Blooms:

California Harmful Algae Blooms Portal:

San Diego Beach and Bay Water Quality Program:

In addition, like so many things there’s an App for that!  The EPA has launched the CyAN app which helps users monitor Harmful Algae Blooms due to Cyanobacteria:


Microcystin toxicity is considered a dangerous medical emergency, so prevention is key.  Stay informed, and if you believe there may be an algae bloom in the water, keep your pet on dry land. 


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