Recognising blue-green algae

By now, you might have heard about blue-green algae and its dangers. But what actually is blue-green algae and how do you spot it? We’ve put together some information you should know.

Blue-green algae is perfectly natural, but can also be dangerous for our four-legged friends (and us)! Our dogs love to swim (mostly) especially in hot weather and you might find them wanting to jump in every puddle and pond they see. But dogs don’t know that blue-green algae is dangerous for both them and us, so we need to be able to spot it and keep them safe.


What is blue-green algae?

Blue-green algae, or ‘cyanobacteria’, is completely natural. Despite the name, blue-green algae isn’t technically algae – it’s a type of bacteria that looks like algae when it clumps together. Just like algae, it forms in water such as rivers, streams, lakes and ponds. Unlike true algae though, some types of blue-green algae are toxic. Even the toxic blue-green algae doesn’t bloom all year round, so there will be times when water is safe but becomes unsafe later in the year when the algae blooms.

Blue-green algae tends to grow in still or slow-flowing water when it gets a bit warmer. This means ponds and lakes are more likely to have blue-green algae than, say, a river. It can also grow in flooded areas where the water has stood for some time.


What does blue-green algae look like and how can I spot it?

Blue-green algae can’t actually be seen until it starts clumping together. Once it clumps, there are a few different ways blue-green algae appears in water:

  • It can look like a green or blueish scum on the water
  • It might look like someone has thrown blue or green paint into the water
  • It might clump together to look like seaweed
  • It can appear in brown clumps alongside other weeds in the water
  • It can appear as green flakes or brown dots
  • It can turn water cloudy and give it a green, blue-green or greenish-brown appearance
  • You might see foaming on the edge of the shore, which can look like sewage pollution.

Some (but not all) blue-green algae species release dangerous toxins into the water. There’s no way of telling if algae is toxic just by looking at it and even blue-green algae isn’t always toxic – some types are safe while others are only toxic at certain times of year when they’re blooming. If you are worried there may be blue-green algae, it’s best to keep your dog well away from the water. Don’t let them touch or drink it.

Sometimes if blue-green algae is present, you might notice dead fish or other wildlife in the water. Never let your dog drink from water with dead fish in it.

Blue-green algae can make water look green, blue-green or green-brown

Blue-green algae can form green scum on the water.

Blue-green algae can clump around other plants and weeds.

How do I know if my dog has blue-green algae poisoning?

Dogs exposed to toxic blue-green algae can become very ill very quickly. We have more information about the symptoms of blue-green algae poisoning and treatment on our Pet Health Hub:

How to protect your dog from blue-green algae

As there’s no way of telling if blue-green algae is toxic just by looking at it, keep your dog away from lakes and ponds where it may be present. It’s not worth the risk. Don’t let them swim in or drink from any water that could have toxic algae in it.

Your local council will put up signs in places that regularly have blue-green algae or in places they know currently have the algae after testing the water. Have a look around and if you see these signs it may be best to keep your dog on their lead so they’re not tempted to go for a swim!

If you spot blue-green algae but there are no signs up, you should report it to the Environment Agency on 0800 80 70 60. They will be able to test the water and put a sign up to warn other people if blue-green algae is found. It’s better to be safe than sorry so if you’re worried, report it.

Keeping cool

Summer is a great opportunity to get out and about with your dog, but remember to keep them cool on the hot days.

Days out

Thinking of visiting a dog friendly beach with your canine pal? Read our tips and advice before you go.