How To Identify Toxic Blue-Green Algae: Keeping Your Dog Safe

women holding dog while sitting in front a lake looking ahead

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The term “blue-green algae” generally refers not to a type of algae, but rather to a toxic type of bacteria that lives in algae, called cyanobacteria.

A rapid increase in the growth of algae is called a bloom. When algae blooms occur, the number of cyanobacteria in the algae increase as well. Water affected by an algal bloom may look pea-green with a thick mat of green or blue-green algae on the surface.

small pond with blue-green algae present.
Small pond with blue-green algae present on the surface. Image Credit: JFLAURIN via iStock / Getty Images Plus

Algal blooms are most commonly found in freshwater sources, including lakes and ponds. They also occur in brackish water, such as where a river meets the sea. It is saltier than fresh water but not as salty as the ocean.

Algal blooms are more likely to occur during the warmer months, when there is an increase in nutrients present in the water, in stagnant water, or during times of low rainfall. However, blue-green algae are found worldwide and are present year-round.

It’s safest to assume that any algal bloom could be toxic—to both pets and people.

Wind can blow an algal bloom to one side of a body of water or push it toward the shore. There may be warning signs posted near bodies of water that have been positively identified as containing toxic cyanobacteria.

Most blue-green algal blooms do not produce toxins; however, a small amount produce vary harmful toxins that can cause life-threatening symptoms or death. Harmful blue-green algae can not only cause severe clinical signs in dogs, but  are also toxic to humans.

Unfortunately, it is impossible to tell with the naked eye if an algal bloom is harmful. Therefore, it’s safest to assume that any algal bloom could be toxic—to both pets and people.

What Is Blue-Green Algae Poisoning in Dogs?

Any exposure to blue-green algae, whether large or small, should be considered a toxic exposure. When a dog drinks or swims in water with toxic blue-green algae, the various toxins produced can affect a dog’s liver, neurologic system, or skin.

If the toxin your dog is exposed to affects the liver, it can cause liver failure within just a few hours. If the toxin affects the neurologic system, your dog can develop signs of neurologic abnormalities within an hour. The toxin that affects the skin does not cause signs as rapidly as the other toxins do, and these are often seen after several days.

Unfortunately, the toxins that affect the liver and neurologic system are typically fatal and can cause death within a few minutes to hours, or within a few days. Dogs exposed to the toxin that affects only the skin usually survive, but treatment is still needed.

Are All Blue-Green Algae Toxic?

Not all blue-green algae are toxic. There are approximately 2,000 species of blue-green algae, and only about 40 species are considered toxic. Although most algae blooms do not produce toxins, it is impossible to specifically visually identify blue-green algae that may be toxic to pets. Therefore, it is important to be wary of all visible algal blooms.

Symptoms of Blue-Green Algae Poisoning in Dogs

Depending on the toxins present in blue-green algae, a dog’s liver, neurologic system, or skin can be affected. Clinical signs may include:

  • Vomiting

  • Diarrhea

  • Drooling

  • Reddening of the skin

  • Blisters of the skin

  • Muscle tremors

  • Muscle rigidity

  • Seizures

  • Inability to walk

  • Difficulty breathing

  • Weakness

  • Death

Because clinical signs can develop rapidly and are life-threatening, if your dog is exposed to blue-green algae, get to a veterinary clinic as fast as possible.

How Do Veterinarians Treat Blue-Green Algae Poisoning in Dogs?

The goals of treatment for blue-green algae poisoning in dogs are to prevent further exposure to and absorption of the toxin, to control life-threatening symptoms, and to provide supportive care. If, after a known exposure to blue-green algae, your dog is not showing clinical signs, the vet may start with inducing vomiting and giving your dog a bath.

Due to the risk of the vomit entering the lungs, which can lead to aspiration pneumonia, never try to induce vomiting in your dog at home.

Typically, dogs who are exposed to toxic blue-green algae need aggressive and intensive care, including medications to control tremors and seizures, fluid support, close monitoring of blood work, medications to support the liver, and potentially placement on a ventilator to help them breathe.

The best way pet parents can keep their pets safe is by keeping them away from water with visible algal blooms.

Unfortunately, because clinical signs of some types of blue-green algae poisoning develop quickly and exposure is usually fatal, treatment tends to be unsuccessful.

If your pet only develops clinical signs that affect their skin, they can survive. In this case, they may need topical ointments, topical antibiotics, or oral antibiotics to treat their blisters.

Can a Dog Survive Blue-Green Algae Poisoning?

The different toxins produced by different species of blue-green algae vary in the clinical signs they cause. Exposure to the toxins that damage the liver or cause neurologic signs typically results in death.

If your dog is exposed to the toxin that only affects the skin, they typically survive, but still require treatment at a veterinary clinic.

Prevention of Blue-Green Algae Poisoning in Dogs

The best way pet parents can keep their pets safe is by keeping them away from water with visible algal blooms. Algal blooms can occur in fresh water, such as ponds and lakes, and in brackish water, such as where a river meets an ocean.

If you are with your pet in any of these areas, it is important to look for visible algal blooms or warning signs indicating that a harmful bloom is present.

Algal blooms occur more commonly during warmer temperatures, so exposure is more common during the summer; however, the toxins have been detected year-round.

Keeping your dog in a harness when they are in or near an open body of water will allow you to gently pull them back from any suspicious plant material.

Because algal blooms have the potential to be so devastating, if you see an algal bloom, it is best to keep your dog away from it and report it to the environmental health section of your local health department.

Pet Poison Helpline Veterinarian Team


Pet Poison Helpline Veterinarian Team


Pet Poison Helpline®, your trusted source for toxicology and pet health advice in times of potential emergency, is available 24 hours,...

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