What is Blue Green Algae?

Blue green algae is a group of bacteria called ‘Cyanobacteria.’

The bacteria can not be seen until it clumps together, when it turns to green flakes or greenish brown dots in ponds, lakes or streams. This happens when the water levels are below normal, the weather has been very hot or there has been a lack of rainfall. The algae blooms and gives a blue-green scum on the surface of non-flowing water, this normally collects around the edges of ponds and lakes where animals are most likely to drink. You may notice dead fish if there is a high concentration of the bacteria.


It is very toxic to dogs and you need to seek veterinary advice if you suspect your dog has been in contact with contaminated water.


  • Vomiting
  • Diarrhoea
  • Seizures / Fitting
  • Weakness / collapse / unconsciousness
  • Disorientating / confusion
  • Drooling
  • Breathing difficulties

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.



Blood and urine tests will be performed to make a definitive diagnosis, if the dog is presented shortly after any suspected water has been drunk the dog maybe made to vomit and activated charcoal given to absorb anything left in the stomach.

Further treatment will depend on the dog and supporting their liver and nervous symptoms. Even if the dog seems to make a full recovery the effect of the poisoning can affect the liver later in their life.

Blue green algae is also toxic to cats if they find contaminated water and again immediate treatment is necessary.

It is also a health risk to humans it can cause a skin rash, sickness, stomach pains, fever and headaches, children are a greater risk.

Keep your dog away from lakes and ponds that you know, or suspect may, contain blue-green algae. Dogs should not be allowed to swim or paddle in water that contains blue-green algae. Suspected water should have warning signs around the area, but if you suspect any of water then this needs to be reported to the Environment Agency who will investigate further.

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