Toxic Blue-Green Algae Can Be Deadly to Your Dog


It’s that time of year again – when news reports start coming out of dogs dying after swimming in or drinking from ponds, lakes, and reservoirs polluted with toxic blue-green algae. The component of the algae that produces toxins is called cyanobacteria.

Three dog deaths in July have been attributed to toxic algae at Grand Lake St. Marys in Ohio, but the problem can occur anywhere. In past years, reports of toxic algae blooms have ranged from California to Maine, and Canada to Florida, as well as the UK.

Blue-green algae thrive in warm, shallow water. While algae may be present throughout the year, it is only when there is an extensive “bloom” that problems occur. Most blooms occur in late summer or early fall, but they can occur earlier as well, particularly when the weather is unusually warm and dry. Toxic algae can be blue, bright green, brown, or red.

Signs of toxicity in dogs may start with lethargy, followed by vomiting and diarrhea. Tremors and seizures can occur almost immediately. Additional signs range from excess salivation, skin irritation, and pale gums to severe respiratory, circulatory, or neurological disorders. Convulsions and death can occur as little as four hours after exposure. Treatment may include fluids to prevent dehydration, diazepam (Valium) to control seizures, atropine to counteract the poison, charcoal to absorb toxins from the stomach, and adrenaline to help counteract respiratory failure.

Prevention is the best course of action. Keep your dogs away from stagnant water in warm weather, particularly if you notice any of the following:


  • The water looks like green paint or pea soup, or is cloudy with a green, yellow, or blue-green hue.
  • It smells swampy or musty.
  • You see what looks like foam, scum, or mats on top of the water.


If contact occurs, prevent your dog from licking his feet or coat, and wash him off thoroughly with clean water as soon as possible. If you suspect problems, contact your vet immediately. If your dog becomes ill, be sure to notify authorities so that warning signs can be posted to protect other pets and people.

More information:

Blue-green Algae and Harmful Algal Blooms

San Francisco Bay Area resident Mary Straus has spent more than a decade investigating and writing about canine health and nutrition topics for her website,


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