What is blue green algae? How to protect your pet from this hidden danger

Written by Napo HQ
Reviewed by Dr Louisa Lane
30th Aug 2022
6 mins read
The photo shows an old yellow Labrador swimming in a lake with green water. Could it be contaminated with blue green algae?
Blue green algae is a group of bacteria that live in slow water, and “bloom” in hot summer weather. These bacteria release toxins into the water which can poison your dog, and cause potentially fatal illness. Never let your dog drink from or swim in water that may contain blue green algae. If you think your dog has come into contact with it, rinse them with clean water and call your vet immediately. This blog was updated on 17th April 2023
Most dogs love a dip in the hot weather, but owners must be careful where they let their pups swim. Many lakes and ponds around the UK are home to blue green algae, which is toxic to dogs and could cause serious or even fatal illness.
To help you protect your pooch this summer, we’ve created a complete guide to blue green algae. Read on to find out what it is, where you find it, what the symptoms of blue green algae poisoning in dogs are, and what to do if your dog gets sick.

What is blue green algae? 

Despite the name, blue green algae is not an algae or a plant. It’s actually a type of bacteria called “cyanobacteria” which lives in water.
Blue green algae can produce toxins that can be harmful to humans and animals if ingested, or if they come into contact with your skin, or your pup's skin.

What time of year is blue green algae in the UK?

Blue green algae is most common in the summer in the UK, typically peaking in mid to late summer. 
However, the bacteria thrive in warm and sunny weather, especially if there hasn’t been much rain. Cases of blue green algae can occur at other times of the year if it’s been particularly warm and dry.

Where is blue green algae found?

Blue green algae can be found in still or slow-moving water throughout the UK. It commonly affects lakes, ponds, canals, and reservoirs. It can also grow in smaller stagnant water sources like bird baths, ditches, and water bowls left outside.
Although it’s often found in stagnant water, it can also be found in some streams and rivers.
Essentially, any water that is slow moving and receives a lot of sunlight can be home to this bacteria.
a map of blue green algae locations
, provided by the centre of UK ecology and hydrology. You can also help to keep people and pets safe by submitting sightings of blue green algae to the app.
the photo shows a scruffy terrier crossbreed playing in the shallow, clear water of a lake

How to identify blue green algae

Signs that water is contaminated with blue green algae include:
  • Cloudy water with a blue, green, or brown tint.
  • Wisps of green or brown scum in the water.
  • Blue or green scum in or on the water. (It can look like spilt paint!)
  • Foamy buildup at the water’s edge.
  • Green or brown flakes in the water.
  • Green clumps and lumps in the water.
To make it even more complicated, some species of blue green algae are harmless, and others are only toxic at certain times of year when they bloom and clump together.
The safest thing to do is to keep your dog away from any water that shows any of the signs listed above. Don't let your dog drink or swim in water you think could be contaminated.

Is blue green algae poisonous to dogs?

Yes, several species of blue green algae are poisonous to dogs and produce toxins that contaminate the water they’re in.
Although it's dangerous to humans and animals, dogs are more at risk because they often play and swim in water during warm weather. Many dogs unwittingly drink from contaminated water, or ingest water while swimming. If your dog swims or plays in contaminated water, the bacteria can stick to their fur, and your dog might ingest them later when they lick themselves clean.
If your dog ingests these toxins, it can cause damage to their liver, kidneys, and nervous system. In severe cases, the toxins can cause liver failure which can put your dog’s life at risk. It may also cause brain damage.

Can blue green algae kill dogs? 

Sadly, cases of blue green algae poisoning are often fatal for dogs. Early, aggressive veterinary treatment can improve your dog’s chances of survival.
However, some dogs that survive can be left with long-term neurological, liver, or kidney damage.

How quickly does blue green algae affect dogs? 

Your dog can become sick very quickly if they’ve ingested contaminated water, and they can show symptoms of illness within 15 minutes to an hour. 
However, illness doesn't always happen quickly. Some dogs might not become sick until a few days after coming into contact with blue green algae.

Can blue green algae affect humans?

Yes, blue green algae can make humans sick if you swim in it or ingest it. So not only should you stop your dog from swimming in contaminated water, you should keep clear too!

Symptoms of blue green algae in dogs

The symptoms of blue green algae poisoning in dogs include:
  • Vomiting (Sometimes containing blood)
  • Drooling
  • Increased thirst
  • Lethargy
  • Difficulty breathing
  • Disorientation
  • Problems standing and moving
  • Collapse
  • Twitches and tremors
  • Seizures
  • Sudden or unexplained death
The photo shows a Belgian Shepherd dog running through a river with a stick in it's mouth

How to prevent blue green algae poisoning

You can prevent your dog from being harmed by blue green algae by making sure they don’t come into contact with contaminated water.
Don’t let your dog drink from water that may contain cyanobacteria, and never let them play or swim in water that may be contaminated.
If you’re near a lake, river, or reservoir, check for signs that warn you if blue green algae is present.
Always rinse or wash your dog with clean, fresh water after they have been swimming outdoors. This can help to wash away bacteria stuck to their fur. When you get home, give them a more thorough wash in the bath.

What should I do if my dog comes into contact with blue green algae?

If you think your dog has come into contact with blue green algae, rinse them with clean water. This will help to remove any bacteria on their fur that they might ingest later when they clean themselves. You should also call your vet immediately for advice. You’ll likely be told to bring your dog to the vets for treatment as soon as possible.

Treatment for blue green algae

There is no antidote for blue green algae poisoning. All your vet can do is to try and remove as many toxins as they can, as quickly as they can, to give your dog the best chance of recovery.
Your vet might try to induce vomiting. Never try to make your dog vomit yourself, as you will do more harm than good. 
They might also feed your dog activated charcoal. This binds with toxins and stops them from being absorbed into the body. Never feed your dog a DIY charcoal treatment, because this could make them sicker. Activated charcoal is specially formulated and prescribed by vets.
Your dog will probably be given oxygen, and intravenous fluids to support the liver and help it to remove toxins from the body.
They will treat any symtpoms your dog has. Your dog may be given medication to prevent seizures and to treat other complications caused by blue green algae poisoning.
Many dogs require intensive care, and sadly, some owners have to face the difficult decision of euthanasing their pets.

Final thoughts

Blue green algae can cause serious illness and can even put your dog’s life at risk. Dogs that survive blue green algae poisoning often face life-long health conditions as a result.
Keep your pet safe this summer
by keeping them away from contaminated water, and always call your vet if you think your dog has been in contact with blue green algae.
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