Posted by Belinda Bird on

Blue-Green Algae is a silent killer for not only dogs, but cats, cattle, sheep, pigs, goats, and any farming animal that has access to it. This seemingly harmless pond flora is known to infect and kill within minutes to hours of ingestion, often not giving owners the time to reach a veterinarian for support. 

To make the fear even more real, this algae can grow in any stagnant or slow-flowing water source. Birdbaths, fish ponds, rivers, dams, plant containers and fountains are all a potential breeding ground, couple these water sources with a hot and humid temperate and you have just created the perfect conditions for this algae to grow, thrive and “bloom”. 



I will be honest and tell you that I did not know about Blue-Green Algae Poisoning until coming across a heartbreaking story on social media about a dog that died before her owner could even make it from the river to the vet. After researching and learning about its extreme level of toxicity not only was my jaw dropped but I started flashing back to all the ponds, dams and lakes that I have seen algae floating in, and with absolutely no idea of the risks.     

For thousands of owners around Australia taking their dogs for a swim today, please share this article so we can make pet parents aware and hopefully prevent some fatal poisonings from occurring. 


Blue-Green Algae is also known as Cyanobacteria and is a microscopic bacteria that is commonly found in areas with stagnant freshwater and brackish (slightly salty) water ecosystems, such as dams, ponds, streams, rivers and lakes. It favours a hot environment, and with summer on its way I want every pet parent to be ready. 

This algae produces toxins (Microcystins and Anatoxins) that are dangerous to people, livestock and pets that swim and drink from the contaminated water source. Not all algae blooms are toxic, but, it is impossible to know if the algae in a particular pond is dangerous without proper testing. Because of this, if you are suspicious you should always err on the side of caution and stop your dog from swimming or drinking the water. Very small exposures of blue-green algae contaminated water, such as a few mouthfuls could result in fatal poisoning.  

Blue-green algae concentrations vary throughout the year but are most abundant during periods of hot weather in mid-to-late summer. Its toxin is known to affect the central nervous system, liver and kidneys, and worse still, the toxins can remain in the water even after the blue-green algae themselves have vanished - in some cases for weeks, depending on the conditions. 

Cats can also be affected by the algae but as cats generally stay away from swimming and are much more strict than dogs with their water source, the risk to them is significantly less. 


Blue-green algae can form vast “blooms”, some large enough to be seen from space! 

Here is an image of a blue-green algae bloom from NASA of Shark Bay, Western Australia, that was big enough to see from space. 




Unbelievable to think that something so individually small, but so deadly is sitting in thousands of ponds, dams, creeks and lakes across Australia, and with such little education on its effects. 

During the summer drought of 2009 and 2010, a total of 1,100 kilometres of the Murray River suffered from major blue-green algae blooms, which hindered the use of water for drinking, agriculture and recreation. It is estimated that millions of fish died as a result. The images below are the Murray River during this outbreak. 



When blue-green algae grow and colonise to form “blooms”, it gives the water a distinct blue-green appearance or a “pea soup” like colour. As you can see in the images above, the colour looks like nothing natural. As the algae grow and create blooms, it floats along the surface of the water and is easily blown by the wind into thick, concentrated mats near the shore, making it easy for animals to access. 

Blue-green algae is more likely to be found in nutrient-rich water, making dams and river systems running along farms an ideal breeding ground. As manure and fertilisers are washed into the water, the more nutrient-rich the water becomes. 

For many years, tracking of blue-green algae was conducted by physically visiting and testing an area for confirmation. While this is successful, it is a slow and inefficient method as it did not do enough to determine the location and drift of a body of water over thousands of acres in size, and simply expanding the number of spot sampling sites would be impractical. 

New satellite technology has found a way to track blue-green algae outbreaks around Australia. Data from satellites is collected and collated, then using an algorithm, a system combs every pixel of an area for signs of toxic algae activity. The technology relies on identifying the levels of total phosphorescence (a specific colour) of every single pixel of a scanned image. In other words, maps that look similar to a heat map show areas of phosphorescence across Australia, allowing researchers to see measurements of chlorophyll-a, cyanobacteria (blue-green algae), and phosphorus in the water. Quite amazing when you think of the impact this can and has had on identifying algae contaminations nationwide.  

Here is an example of a map produced by Blue Water Satellite, depicting phosphorus concentrations in Maumee River




The biggest piece of information to take out of all of this is… if you suspect the water is contaminated by blue-green algae, do not allow your dog to swim, drink or play in the water! 





Blue-green algae produce two types of toxins, microcystins and anatoxins. The severity and symptoms depend on which of these two toxins is ingested. In short, Microcystins affect the liver and Anatoxins target the nervous system. 





Microcystins severely affect the liver, causing organ failure. With so many systems within the body depending on the liver to function a large range of symptoms is normally seen. The liver is a filter for toxins and metabolic by-products from the body and failure to do this effectively results in a build-up of toxins that cause neurologic signs such as disorientation and seizures, which can lead to shock and/or comatose. As the liver continues to fail, death is imminent within days. Death can occur between 12-24 hours after ingestion. 




It may not seem possible, but the effects of Anatoxins is much more severe. After ingestion, signs of poisoning are known to often occur within 30-60 minutes of exposure and focus on targeting the nervous system. Toxicity in animals displays as hypersalivation (excessive drooling), overproduction of tears, muscle tremors, while some muscles become very rigid or paralyzed. 


A lack of oxygen causes blue gums and paralysis of the diaphragm results in respiratory failure and death. Exposure to Anatoxin causes a rapid death and has been seen within minutes to hours after exposure. Livestock that drank from a contaminated water source are often found dead right beside the edge of the water. 





The symptoms are different depending on the type of algae ingested. If your pet is displaying symptoms and he has been swimming in suspected water, see a veterinarian immediately. 


  • Weakness
  • Lethargy
  • Lack of appetite
  • Vomiting
  • Diarrhoea (dark, tarry stool)
  • Bleeding
  • Pale gums
  • Jaundice (yellow tint to gums and skin)
  • Shock
  • Seizures
  • Collapse and coma
  • Death




  • Weakness or inability to walk
  • Excessive salivation
  • Excessive tearing
  • Difficulty breathing
  • Blue discolouration of the skin and mucous membranes
  • Tremors
  • Seizures
  • Muscle rigidity
  • Paralysis
  • Disorientation
  • Coma
  • Death

(List of symptoms collected from:






Immediate treatment is vital for any chance of survival. This toxin is extremely fast-acting making speedy intervention is essential. 

If caught before symptoms are shown, hospitalisation can help and is focussed on ridding the body of the toxin. There is no “antitoxin” for blue-green algae, meaning that treatment involves using supportive measures to help reduce the level of symptoms seen. Your vet may induce vomiting to rid the stomach of the algae or give oral charcoal in an attempt to absorb the toxin. Gastric lavage (pumping of the stomach) may also be a measure considered by your veterinarian. 

Unfortunately, symptoms are often seen before medical treatment is sought, meaning it more often than not results in a fatality. Treatment is limited to supporting the organ system that is being affected and displaying symptoms. 

With more severe symptoms, aggressive therapy may be required, such as IV fluids and plasma to replenish electrolytes and regulate blood glucose. Muscle relaxers are designed to help with muscle tremors and anti-seizure drugs are given for convulsions


The number one way to ensure the safety of your pet is by not allowing them to swim in water that appears to be discoloured with a green tinge, or has algae visibly floating on the surface. Remember, it only takes a few mouthfuls of water for a potentially lethal dose!

It is always best to carry a few treats with you on a walk so you can distract your pet quickly if necessary. For example, if you normally allow your dog to swim in the river near your home and one day you see some floating algae, it could be difficult to gain his attention and distract him away from the water's edge. Most dogs respond fast to a treat that is being waved in front of their nose, and it could be the distraction you need to prevent a horrific accident. 

As blue-green algae thrive in nutrient-rich water, growing vegetation around lakes, rivers, ponds and dams can be beneficial in stopping fertiliser runoff into the water. 

Fence off contaminated areas to prevent livestock from drinking affected water, and provide fresh water sources for all animals. 

Not all types of algae are deadly, but without specific analysis, it is difficult to differentiate between algae that is poisonous or not. It is safe to assume that all algae blooms are dangerous and avoid contact completely. 






If you have any experiences that you would like to share, or have any questions, please reach out to me. I would love to hear from you. 



Belinda Bird

Founder & Veterinary Nurse



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Created on Posted by Innate Pets Comment Link

Thank you! I am glad that you found it informative Mia. I had no idea either. Scary isn’t it!

Created on Posted by Mia Comment Link

Thank you for sharing. I had no idea!

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