What is it?

Blue-green algae is a term used to describe a group of bacteria, called cyanobacteria. They are not actually algae, but the organisms got this name because they often give the appearance of algae when they clump together in bodies of water.

They cannot be seen with the naked eye unless they clump together. When this happens, blue-green algae can look like green flakes, greenish bundles or brown dots in a pond, lake or stream.

When the algae blooms, it can give look like a blue-green scum has appeared on the surface of the water. Blooms of the organisms often build up around the edges of ponds and lakes, which may look like foam.

It is most common in non-flowing fresh water such as lakes and ponds during hot weather when there is less rainfall, but can also occur at other times of the year right up until the winter.

The algae may be present in a harmful form even if you cannot see it, so if in doubt don’t allow your dog to swim in ponds and lakes in particular.

Why is blue-green algae dangerous to dogs?

Blooms of blue-green algae can produce harmful toxins which stop a dog’s liver from functioning properly. However, not all types of blue-green algae are dangerous.

Sadly, exposure to toxic blue-green algae is often fatal, and can also cause long term health problems in dogs that survive after drinking or swimming in algae-contaminated water. Some types of blue-green algae can kill a dog just 15 minutes to an hour after drinking even the smallest amount of contaminated water.

Dogs who have been swimming in water can get the algae caught in their fur, and can ingest it while cleaning themselves later on.

What are the symptoms of blue-green algae poisoning?

If your dog shows any of the following signs after drinking from, or swimming or paddling in water, contact your vet immediately and tell them you are concerned about blue-green algae:

  • Vomiting/being sick
  • Diarrhoea
  • Seizures/fitting
  • Weakness/collapse/unconsciousness
  • Disorientation/confusion
  • Drooling
  • Breathing difficulties

There is no antidote for the toxins produced by the bacteria, but if caught early enough, your vet will likely try to make your dog sick and attempt to flush the toxins from the body before they take hold.

Sadly, blue-green algae poisoning often eventually causes fatal liver failure.

These symptoms are commonly seen with other illnesses too, which are often less serious, but you should always call your vet if you are worried your pet is sick.

How can I protect my dog from blue-green algae?

Keep your dog away from lakes and ponds that you know, or suspect may, contain blue-green algae even if you can’t see it.
Dogs should not be allowed to swim or paddle in water that contains blue-green algae.

Don’t let dogs drink from water that may have blue-green algae in. Because the wind often blows blooms of algae to the edges of ponds or lakes, higher concentrations of the toxin are more likely to be present in the parts of the water your dog may drink from.

Take note of signs warning of the algae during dog walks and follow the information given.

Can my cat be affected by blue-green algae?

Yes, blue-green algae is toxic to cats. Contact your vet immediately if your cat drinks from water contaminated with blue-green algae.

Is blue-green algae a health risk to humans?

Yes, blue-green algae can cause skin rashes, sickness, stomach pains, fever and headaches in humans. There have been some reports of more serious illnesses including liver and brain damage. Children are at greater risk than adults. Don’t drink from or enter this water.

If you think you have spotted blue-green algae in water and cannot see any signage, report it to the Environment Agency (0800 80 70 60) who can investigate.