Dog Blue Green Algae Poisoning: a true summer danger

Dog blue green algae poisoning is a serious and potentially deadly risk in the summer months where little rain and warm temperatures allow algal blooms to form in lakes, ponds and slow flowing rivers.  If your dog enjoys swimming or if you walk your dog near any water then you need to know about the risk of blue green algae to your dog


Blue-green algae poisoning is just one of the hot weather summer risks that I discuss in my free hot weather dog care ebook which you can download here.

What is blue-green algae?

Blue green algae are actually a group of bacteria known as cyanobacteria that are found in freshwater rivers, streams and ponds as well as brackish, or slightly salty, water.  While they are normally present, they are only found in very low numbers and don’t normally pose any kind of danger. They are also microscopic and invisible in normal conditions.

When condition are right however, when water levels drop, water flow slows and temperatures rise, the conditions are right for an explosion in growth.

This results in algal blooms where the blue green algae numbers increase dramatically.  This can be seen in two ways. The algae may clump together and float, forming bluey-greeny-brown flakes or mats.  Rather than solid mats the water may also take on a discolored pea-soup appearance or have a blue-green-brown foamy scum on the surface.

Blue green algae blooms are more likely to form in low lakes, ponds and rivers in hot weather during low rainfall

These mats or foam most commonly develop in still water, so lakes and ponds, but rivers can definitely be affected if the water is slow flowing or there are backwaters and other pockets of still water present.  In fact, several of the rivers near me develop blue green algae most years towards the end of the summer.

Not every waterway will be affected.  These blue green algal blooms are also more likely to be found in nutrient rich water, such as that where there is water runoff from farmland.

Why is blue green algae poisonous?

Now not all cyanobacteria produce toxins but if you see these blooms in the water there is simply no way to distinguish safe from dangerous forms by sight alone.  If you see any sign that blue green algae is present then you must assume that it is the dangerous type.

This is because other cyanobacteria produce deadly toxins.  Some poisonous blue green algae produce neurotoxins that affect the bodies nervous system, others produce a toxin that destroys the liver.

To make matters worse, only a really small amount of water containing the toxin needs to be drunk.  A couple of mouthfully may be all that is needed to result in fatal poisoning.

So now you know what blue green algae looks like (and you can see a few pictures here) and why it can be deadly.  Just what then are the signs and symptoms of blue green algae poisoning in dogs?

Signs of poisoning in dogs

Well, the poisons may only take 15-30 minutes to start working and causing your dog to start experiencing signs of poisoning.  This means that you may notice your dog becoming unwell while you are still on your walk or shortly after getting back home.

If the cyanobacteria are producing neurotoxins then these attack the bodies nerves.

Signs of poisoning with a neurotoxin can include:

  • excessive salivation

  • muscle tremors and twitching

  • rigidity with the legs becoming stiff

  • seizures and fitting

  • Paralysis

  • difficulty breathing as the chest muscles and diaphragm stop working

  • Blue-tinged gums

Death may only take minutes to hours.  This poison works very quickly and is deadly.

Blue green algae poisoning only takes a couple of mouthfuls and can kill in minutes

If the cyanobacteria are producing hepatotoxins then these attack the liver.

Signs of poisoning with a liver toxin are:

  • Vomiting

  • Diarrhoea

  • bloody or black stools

  • pale or yellow gums

  • Weakness

  • Seizures

These signs are likely to take longer to show and death is more drawn out, taking a couple of days.


Blue-green algae can kill your #dog in minutes.  Learn the risks and how to keep your dog safe this summer

Treatment and prevention

How then can blue green algae poisoning in dogs be treated?  Unfortunately there is no antidote once poisoning had occurred.

Treatment immediately after exposure is vital but even then, the prognosis is poor if a fatal amount of poison has been consumed.  Your vet may make your dog sick to remove any toxin still present in the stomach (although this won’t be done if your dog is showing nervous signs of poisoning) and supportive treatment will be given to try and limit the damage and effect of any toxin.

For those dogs that don’t die, the likelihood of a complete recovery is very good but given the fact that only such a small amount of poison is needed to be fatal, even with immediate treatment death is very likely.

As with most things, prevention of blue green algae poisoning is always the best course of action:

  1. Remember what blue green algae looks like and avoid letting your dog into any water that looks remotely suspicious.

  2. Be aware of the local risks - certain waterways are more likely to be a poison risk than others.

  3. Local councils and environmental agencies are very likely to monitor and sample local water conditions and publish where blue-green algae is present.

  4. Your vet may know which areas to avoid.

  5. If in doubt, during hot weather with low rainfall do not let your dog in any water, especially lakes, ponds and small slow flowing rivers.

Also be aware that blue green algae is toxic to humans and other animals.  You should not swim or even paddle in suspect water.

Make sure you download my free ebook to help avoid the risk of heatstroke and other hot weather dog dangers

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