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Cornell Richard P. Riney Canine Health Center

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Blue-green algae poisoning: Cyanobacteria toxicosis


Blue-green algae is a toxin-producing cyanobacteria that can be found in lakes, ponds and rivers. Exposure to toxins produced by these bacteria can be life-threatening to dogs, humans and other animals. There is no antidote for blue-green algae poisoning, and it can rapidly become fatal. Preventing exposure is the most effective way to avoid this deadly toxin. 


Blue-green algae poisoning (or cyanobacterial toxicosis) occurs when dogs drink or swim in water contaminated by an algal bloom. Algal blooms are an overgrowth of cyanobacteria that can produce numerous types of toxins (specifically, cyanotoxins). The two most serious types of cyanotoxins (called microcystin and anatoxin), can cause liver or neurologic injury. Shock, liver failure, respiratory arrest and even death can occur.  

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.  

Clinical signs 

The clinical signs for cyanobacteria toxicosis will vary depending on the specific toxins in the water. The two most dangerous toxins affect the nervous system and the liver.  

Clinical signs can develop rapidly or over several hours, and may include any of the following: 

  • Vomiting 

  • Diarrhea 

  • Weakness 

  • Pale gums 

  • Collapse  

  • Drooling 

  • Muscle tremors 

  • Difficulty breathing 

  • Muscle rigidity  

  • Paralysis 

  • Seizures  

  • Sudden death 


An initial diagnosis is made based on the presenting clinical signs and any history of exposure to water that may have contained an algal bloom. Water may be tested for cyanobacteria toxins to confirm a diagnosis.  

Your veterinarian will recommend blood work to look for signs of organ injury. They may also test for blood clotting abnormalities if the liver is damaged. 


Initiating treatment as early as possible after exposure to blue-green algae is critical. There is no specific antidote for cyanotoxins, and treatment involves intensive, supportive care for patients experiencing shock or respiratory arrest.  

Treatments may include: 

  • IV fluids 

  • Oxygen 

  • Anti-seizure medication  

  • Electrolytes and glucose  

  • Blood products (e.g., whole blood or fresh frozen plasma) 

Additional treatments may include anti-nausea medications, antibiotics, liver supplements, muscle relaxants and atropine. Your veterinarian will monitor blood work during treatment and adjust medications as necessary.  

Decontamination of patients exposed to blue-green algae may not be performed because patients are usually in critical condition by the time they arrive at the hospital. If the patient is stable early after exposure, decontaminating may include bathing, inducing a patient to vomit, stomach pumping (gastric lavage), activated charcoal or a medication called cholestyramine. Activated charcoal may not be as effective for microcystins (liver cyanotoxin). 


Cyanobacterial toxicity can be devastating. Many patients exposed to cyanotoxins affecting the liver or brain may not survive before arriving at a veterinary hospital, and they will require intensive care if they do.  

Treatment should be initiated as soon as possible to improve the chances of survival. Even if a dog survives the initial exposure to liver cyanotoxins, they may still suffer from chronic liver disease, for example.  


  • Avoid drinking from or walking and swimming in water that has visible algal blooms, scum, foam on the surface or that has an odor.  

  • Check local advisories for warnings before visiting a particular body of water.  

  • Remove stagnant water (plant containers, birdbaths, fountains, etc.) to prevent blue-green algae growth around the home.  

  • If you think your pet may have been exposed to an algal bloom, rinse their fur with fresh water and bring them to a veterinary hospital immediately. 

There is no way to tell the difference visually if a particular bloom is toxic or non-toxic. If you suspect that there may be a possible cyanobacterial bloom, alert the public health authorities at your local or state health department. 

Learn more about freshwater harmful algal blooms on the Animal Health Diagnostic Center's website.