Toxic Algae Blooms Harmful to Pets

Harmful Algae Blooms are caused by an overgrowth of naturally occurring cyanobacteria, which live in fresh, salt, or brackish water. These overgrowth events or algal blooms tend to occur when the water is warm, stagnant and full of nutrients such as fertilizer, farm runoff, or storm drain discharge.

When a cyanobacteria bloom occurs, you cannot necessarily tell by examining the water. That said, such blooms can sometimes cause green, blue, red, or brown water discoloration. Cyanobacteria contaminated waters frequently occur following heavy rainfall and may be associated with dead fish or rotting vegetable odors.

My Dog Swims in Natural Waters. Should I Be Concerned?

Warm, stagnant bodies of water may be filled with a variety of disease-causing organisms, especially when they are filled by waters draining from cities, fertilized soils, and farm environments. Increasing water temperatures and nutrient content mean suitable conditions for harmful algal blooms in fresh and salt waters. It is best to avoid water that appears scummy, unclear, warm, stagnant, or covered with foam. While cyanobacteria do not directly cause infections, they can make large amounts of toxins called cyanotoxins. These toxins can damage the brain, liver, and skin, resulting in sickness or death. The most commonly affected animals drink or swim in water during or just after an algal bloom. Severe symptoms can occur within an hour of drinking or bathing in contaminated water.

Difficult to Detect and Treat

There are no known antidotes to cyanotoxins. The toxins cannot be eliminated by boiling or filtering contaminated water. If you think that your pet has been swimming in contaminated water during an algal bloom, immediately bathe them with clean water. Even licking or grooming themselves after bathing in contaminated water can cause serious illness. Signs associated with cyanobacteria-contaminated water or food consumption may include vomiting, drooling, convulsion, tremor, Seizure, or weakness. These signs often occur rapidly – sometimes within an hour of the initial exposure.

Unfortunately, there are no at-home tests for cyanotoxins, which may be difficult to detect. State and local public health agencies often issue red tide/cyanobacteria warnings around common swimming locations if they are known to contain harmful algal blooms. These harmful algal blooms can be prevented by reducing fertilizer use, maintaining sewers/septic systems, or allowing plants, trees, and bivalve muscles to grow near the water’s edge.  

A Special Risk for Dogs

Dogs are more susceptible to cyanotoxins than humans because they are attracted to the odor of contaminated waters; this means that dogs are often willing to drink, eat, and bathe in water containing fatal concentrations of toxins. Dogs will sometimes scavenge dead fish, birds, or mats of dead plants following a harmful algal bloom. Any food obtained from contaminated water should also be considered unfit for consumption.

A Human Health Hazard

Other animals, including fish, birds, livestock, wildlife, and humans, may be affected. Fish and shellfish from affected areas may be harmful to you or your pet. Because cyanotoxins can cause sudden illness and death, seek immediate medical attention if you or your pet is feeling unwell. More information may be found at

If you have any questions or think your pet may be sick because of a harmful algal bloom, I recommend calling one of our offices to schedule an appointment with a member of our Veterinary Hospital.

   Hal Wrigley VMD