You may have seen stories in the news recently about dogs who suddenly died after swimming in lakes, ponds or rivers containing blue-green algae. To avoid a similar tragedy happening to your pet, we’ve compiled the following information about this poisonous algae and what you can do to protect your pets.

What is blue-green algae?

Blue-green algae is the common name for cyanobacteria, which are microscopic organisms found naturally in all types of water. Cyanobacteria grows rapidly in warm, nutrient-rich environments. It is not technically an “algae” at all – the bacteria was given that name due to the fact that it clumps together in the water, resulting in “blooms” that resemble algae.

Cyanobacteria can take a number of forms and appear in a number of colors (not just the blue-green of its name). According to the Cornell University College of Veterinary Medicine:

“Algal blooms can be found in stagnant water, especially during warm weather spells or after periods with a noticeable lack of rain. They may appear as either blue-green or red-brown colored blooms, mats, foam or scum on the water. The water may also smell of rotting plant material. “

Blue-green algae blooms are most commonly found in late summer and early fall, due to the warmer weather. They also thrive in areas where fertilizer runoff and sewage seeps into the water.

Harmful Algal Bloom in Western Basin of Lake Erie: July 2, 2018, (Photo Credit: Aerial Associates Photography, Inc. by Zachary Haslick)

Why is blue-green algae dangerous?

Blue-green algae is dangerous because it can produce certain natural poisons called cyanotoxins. Skin exposure to cyanotoxins can cause rashes and hives. If ingested, cyanotoxins can cause vomiting, diarrhea, headache and liver damage. Not all blue-green algae releases cyanotoxins. However, it is impossible to spot the difference between the toxic and non-toxic blooms with the naked eye.

What are the symptoms of blue-green algae poisoning in dogs?

According to the Cornell University College of Veterinary Medicine, the following are some of the common symptoms of blue-green algae poisoning in dogs:

• Vomiting
• Diarrhea
• Blood in stool or black
• Tarry stool
• Weakness
• Pale mucous membranes
• Jaundice
• Liver Damage/Failure
• Tremors
• Seizures
• Disorientation
• Coma
• Muscle rigidity
• Paralysis
• Blue discoloration of the skin and mucous membranes (Cyanosis)
• Difficulty breathing

Sadly, blue-green algae poisoning in dogs can result in death, as in two tragic cases in California and Texas that made headlines in the summer of 2024.

What can happen if my dog ingests blue-green algae?

Unfortunately, there is no way to reverse the damage cause by ingesting the cyanotoxins found in blue-green algae. If you suspect that your dog has ingested water containing blue-green algae, contact your veterinarian or visit your local emergency veterinary hospital as soon as possible. If caught quickly, the vet may be able to flush out the toxins before the fatal damage can occur.

Is blue-green algae harmful to humans?

Blue-green algae poisoning is more common in dogs than humans, as dogs are more likely to swim in waters containing this algae. Humans are often reluctant to swim in these waters due to the discoloration and unpleasant smell. Dogs are also far more likely to ingest this water than humans when swimming. Finally, dogs can continue to ingest blue-green algae by grooming themselves after swimming (i.e. licking their fur and paws).

How can I protect my dog from blue-green algae?

The best way to protect your dog from coming into contact with blue-green algae is to not allow them to swim or drink from any water you suspect may contain this hazardous bacteria. Be alert for signs of blue-green algae during any trips with your pup to the beach, lake, pond or hiking trail. If your dog wades into any questionable water, do not let them lick their paws and fur, and be sure to rinse them off thoroughly as soon as possible with clean water.

Blue-green algae can also appear closer to home. Check your pools, decorative ponds and any standing water in your backyard for algae blooms, and if spotted, keep your family and pets away from this water until it can be cleaned. (If you are a DogWatch Hidden Fence customer, contact your local Dealer about adjusting your fence to keep your dog out of these areas.)

Always pay attention to any posted signs or news reports warning of blue-green algae, and contact your local or state health department for more information.

Thanks for reading, and we encourage you to share this information with your fellow dog parents.

Resources:
Cornell University College of Veterinary Medicine
CDC Topics – Harmful Algal Blooms (HAB)-Associated Illness
Minnesota Pollution Control Agency
“Blue-green algae and its dangers to dogs” from Blue Cross for Pets UK
“Recreational water and health: Cyanobacteria and their toxins” from Canada.ca