Blue-green algae and dogs


By Marijo Leroux, animal behaviourist, pet therapist and behavioural groomer

Remember the blue-green algae crisis that hit many of our waterways back in the early 2000s? I do, because dozens of lakes in my neck of the woods here in Quebec were closed to swimming. Strangely, we don’t seem to hear as much about blue-green algae these days. And that’s a shame, because they pose a real risk to both us humans and our faithful companions.

Blue-green algae are microscopic plant-like organisms that occur naturally in ponds, rivers, lakes and streams. Also known as cyanobacteria, these algae have been around for some three billion years. In Canada, they reproduce during the hot summer months. And the hotter and more humid it is, the more they reproduce.

When found in large quantities in water, blue-green algae form green-coloured “blooms” that sometimes look like a paint spill or broccoli soup. More concentrated blooms can also create visible surface scum.

©Photo: GettyImages

Blue-green algae may occur naturally in water, but human activity can also trigger blooms—such as farming activities that release large amounts of nitrogen and phosphorus into the aquatic environment or lawn fertilizers that seep into nearby bodies of water. Discharge from septic systems and municipal or industrial wastewater can also lead to blooms.

What makes cyanobacteria so dangerous is the toxins they contain. While no serious cases of poisoning have been reported in humans, it’s best to avoid all direct contact. Common symptoms of skin contact or ingestion in humans include skin irritation, stomach aches, headaches and sometimes fever. While not dangerous, these symptoms can certainly be unpleasant. Bottom line: never intentionally ingest water containing cyanobacteria, even if you boil it first. Boiling does not purify water containing blue-green algae. On the contrary, it only increases its toxicity.

A good rule of thumb is to always stay at least three metres away from blue-green algae. If you’re fishing in water containing cyanobacteria, avoid eating the fish viscera (such as the liver) to avoid ingesting the cyanobacteria.

For our four-legged friends, cyanobacteria poisoning is much more serious. In 2018, three dogs were poisoned by blue-green algae along the banks of the Saint John River in Fredericton, New Brunswick. Despite their best efforts, veterinarians were unable to save these animals.

For our four-legged friends, cyanobacteria poisoning is much more serious.

Cyanobacteria contain three toxins that are particularly harmful to pets:

1. Endotoxins, which cause skin inflammation or canine dermatitis. While reactions are generally benign, veterinary treatment is usually needed to relieve inflammation and pain.

2. Neurotoxins, which attack the animal’s nervous system. These toxins can cause dogs to produce excess saliva, a condition known as hypersalivation. Dogs can also experience seizures and have difficulty breathing. This lack of oxygen can cause their gums to turn bluish and, in  the most severe cases, paralysis of the respiratory muscles, leading to death. The onset of symptoms is quite rapid—within 20 minutes to 1 hour of ingesting the contaminated water.

3. Hepatotoxins, which attack hepatic function (the liver). In dogs, these toxins can cause vomiting and bloody diarrhea as well as pale or yellowish gums and mucus. Pets may also experience general weakness. Liver damage from these toxins can lead to hemorrhaging and death. Symptoms usually appear between one and four hours after ingesting and/or coming into contact with blue-green algae.

There is no specific treatment for cyanobacteria poisoning in pets. Your veterinarian can only treat the symptoms and administer medications to induce vomiting to flush out the toxins.

The good news is that direct contact doesn’t mean certain death for your pet. Physiological reactions will depend on the concentration and type of toxins contained in the blue-green algae, and whether the pet ingested or simply came into contact with the toxins.

Since blue-green algae are mainly found in stagnant water and along the shoreline, a little prevention can go a long way toward protecting your pet. Before letting your dog in or around a lake or stream, consult a reliable source to find out the current condition of the water, as well as which areas are safe and which ones aren’t. Be attentive and observant. Never allow your dog to drink or swim in standing water. Respect safety instructions; some sites post warning signs alerting visitors of certain risks. Always rinse your dog with clean water after swimming.

You can also alert your province’s local health unit if you spot blue-green algae. This will allow the authorities to test the water and take the necessary measures.

©Photo: GettyImages

To start the season off on the right foot, check out my other articles on life jackets for dogs and how to teach your dog to behave on a boat. You can find them on the Club APRIL Marine website. Have a great summer out on the water!

Malou comportement canin

Club APRIL Marine members get 15% off canine behaviour consultations. Contact Marijo Leroux at