The Dangers of Blue-Green Algae for your Pet

If you’re the kind of person who likes to spend time with your pets in the Great Outdoors, you may have heard of something called blue-green algae. Perhaps you know that they grow in water. You might even know that they can be quite harmful to animals. However, if you haven’t heard of blue-green algae, or would like to know more about them in relation to your pet, this article will explain what blue-green algae are, why they are dangerous, and how you can protect your pets from them.


What Are Blue-Green Algae?

Blue-green algae is a rather inappropriate name – they are not algae and are not always blue-green in colour. Firstly, blue-green algae are actually a kind of bacteria, called cyanobacteria – these bacteria are unique in that they can photosynthesise like plants, producing oxygen from carbon dioxide. In fact, scientists believe that billions of years ago, cyanobacteria were responsible for producing the oxygen in our atmosphere that allowed complex life to form. They also passed on this photosynthesising ability to all plants. So we have cyanobacteria to thank for first creating our oxygen, and continuing to do so via plants.

So that’s all very interesting, but what about cyanobacteria in the 21st century? Cyanobacteria live in fresh water: lakes; ponds; rivers; reservoirs; ditches; and so on. As bacteria are microscopic, you will usually not see cyanobacteria in water. However, when conditions are right (hot weather, slow moving water, and lots of nutrients), the bacteria ‘bloom’. This is where they rapidly multiply to form huge colonies, which become visible on the surface of the water as blue-green-brown foam or scum. These blooms are when blue-green algae become dangerous.


The Dangers of Blue-Green Algae

The primary danger blue-green algae pose to our pets are from ‘cyanotoxins’. Cyanotoxins are a group of toxins, produced by many cyanobacteria, which cause a number of conditions in pets, wildlife and even people. The main areas affected are the liver, nervous system and skin.

Toxins affecting the liver (hepatotoxins) lead to vomiting and diarrhoea, bloody stools, weakness and disorientation, pale or yellow gums and lips, seizures, coma, and ultimately death from liver failure if left untreated. Toxins affecting the nervous system (neurotoxins) cause excessive drooling and tear production, muscle tremors, paralysis, difficulty breathing, discoloured skin, lips and gums, and finally death due to respiratory failure. Toxins affecting the skin (dermatoxins) are not as deadly, but can cause intense itching and redness. So overall, cyanotoxins are nasty chemicals.

Cyanobacteria and their toxins are also a danger to creatures living in the water as well (something to consider if you own a fish pond). To make things worse, as algal blooms die off, the cyanobacteria cells break down, releasing even more toxins into the water. The final nail in the coffin is due to the oxygen in the water being used up as the cyanobacteria decompose, meaning any life that survives the toxins will likely die from oxygen starvation.

There are many different species of cyanobacteria, and not all produce cyanotoxins. However, as there is no way to tell which are harmful or not just by looking at them, it is best for your pets to avoid water with algal blooms in altogether.


Preventing Cyanotoxin Poisoning

Perhaps by now you are in a bit of a panic about letting your pets anywhere near water! Do not be so worried: we have some tips you can follow to prevent your pets becoming poisoned, as well as advice for anyone who owns water likely to have cyanobacteria in it.

The number one rule is to never let pets drink from, or swim in, any water with obvious blue-green algal blooms. If the water is green, murky and has scum floating on top, don’t go near. Another good indicator is looking out for any dead fish or animals nearby – they may have ingested the toxins and died, meaning the water is not safe. In publicly owned areas, warning signs may be put up around water suspected of having algal blooms, so make sure you take heed.

If you do decide to let your pet have a swim, make sure you wash them thoroughly when you get home, even if the water appeared clean. Hopefully the water you let them swim in was clean enough not to contain high concentrations of cyanotoxins, but even a small amount trapped on the fur can cause irritation, or be ingested whilst grooming. Keep a close eye on your pet following a swim, so you can have an early warning if anything isn’t quite right.

For owners of ponds or similar, there will be a few cyanobacteria present. However, this is normal, and is not necessarily a danger. The best way to avoid the bacteria blooming is to keep your water clean. Make sure it is filtered regularly, and there are no chemicals leaking into it – fertilisers are full of nutrients and can often trigger algal blooms. If your pond does unfortunately bloom, there are a number of products you can purchase to help kill the algae. Cover your pond if possible, to prevent any pets or wild animals getting to it while the bacteria are blooming.


Treating Poisoned Pets

Even with the best attention in the world, your pet can come into contact with blue-green algae and their toxins, and become ill. Outdoor cats especially can be hard to keep from infested water. Should you suspect cyanotoxin poisoning, contact us immediately – as with all poisonings, the earlier we can help treat your pets, the better.

At the practice, we may want to confirm poisoning with blood or urine testing, but often it is better to assume they are poisoned, so no time is wasted. Drugs can cause your pet to vomit up the toxin, or activated charcoal can be given to absorb the toxin from the stomach – again, the earlier these are given, the less toxin will be absorbed into their body. After this, treatment mainly involves managing the symptoms. This will likely involve oxygen, pain relief, fluids, anti-seizure medication, and nursing. There are no anti-toxin drugs available, so your pet will have to remove the rest of the toxin from their body themselves.

Outcomes for severe poisoning are usually not positive, and animals will often sadly die if we do not get to them in time. And even with the best care, there is no guarantee on surviving it. This is why we want to emphasise why prevention is so crucial with blue-green algae. The more you can do to prevent accidental ingestion, the better.



Not all blue-green algae are bad; in fact, you may have eaten some yourself as the health supplement ‘Spirulina’. However, when cyanobacteria bloom in water, you can never be sure if they are harmless or deadly. Be very cautious before letting cats outside, or your dogs off the lead, when you know there is water about, and always take a good look at the quality of the water before swimming. Hopefully after reading this article, you are all clued up about these strange bacteria, and will make sure that you and your pets stay safe around water this summer.