Blue-green algae: Why is it dangerous for dogs? A guide for pet owners

Warm weather often means longer walks, countryside adventures and days by the water with your dog. But from spring through early autumn, blue-green algae becomes a serious hazard that every dog owner should be aware of. Found in ponds, lakes and slow-moving water, it can be extremely toxic, and dogs can become very unwell in a short space of time.

At St Kitts Vets, we believe that prevention starts with awareness. This guide explains what blue-green algae is, why it’s dangerous and what to do if you think your dog has been exposed…

What is blue‑green algae?

Despite the name, blue‑green algae isn’t actually algae at all, it’s a type of bacteria called cyanobacteria. It thrives in warm weather and is most common in stagnant or slow‑moving water.

You might notice it as a green, blue‑green or brown film on the surface, sometimes looking like paint, foam or thick scum. The water may also appear cloudy or have an unpleasant smell. Even if you can’t see it clearly, harmful toxins may still be present.

Why is it dangerous for dogs?

Dogs are naturally curious around water. They may swim, paddle, drink from it or lick their fur afterwards, all of which can lead to exposure.

The toxins produced by cyanobacteria can affect the body very quickly, targeting:

• The liver
• The nervous system
• The digestive system
• The skin and eyes

In severe cases, poisoning can become life‑threatening within hours.

Symptoms to watch for

Signs of poisoning can appear rapidly, sometimes within minutes. Symptoms vary depending on the amount ingested and the type of toxin involved.

Common signs include:

• Vomiting or diarrhoea
• Excessive drooling
• Weakness or collapse
• Tremors or seizures
• Difficulty breathing
• Confusion or unusual behaviour
• Extreme tiredness

If your dog shows any of these symptoms after being near water, contact a vet immediately.

Where is blue‑green algae found?

In the UK, it’s most common from late spring to early autumn. It tends to grow in ponds and lakes, reservoirs, canals, slow‑moving rivers and some garden ponds.

Warning signs are sometimes displayed, but blooms can appear quickly, so always check the water before letting your dog go near it.

How to protect your dog

The safest option is to avoid any water that looks suspicious. If the surface appears scummy, discoloured or stagnant, keep your dog well away.

A few simple precautions can help:

• Bring fresh drinking water on walks
• Avoid letting your dog swim in unfamiliar ponds or lakes
• Check local alerts if you regularly walk near water

When in doubt, choose caution and move on.

What to do if your dog has been exposed

If you think your dog has come into contact with contaminated water, act quickly. Move them away from the area straight away and try to stop them licking their fur. If you’re able to, rinse their coat with clean water to remove any residue.

Once they’re safe, contact your vet for advice. Don’t wait for symptoms to appear, early treatment gives your dog the best possible chance of recovery.

How is poisoning treated?

There is no specific antidote for blue‑green algae toxins. Treatment focuses on supporting your dog and managing symptoms.

Depending on the severity, your vet may provide fluids, medication, oxygen therapy and close monitoring. Some dogs require intensive care, especially if the liver or nervous system is affected.

Staying alert to seasonal risks

Blue‑green algae is a seasonal risk that can become serious very quickly, but fast action can save lives. If your dog has been swimming in suspicious water, has drunk from a pond, or seems unwell after a walk, contact us straight away.

Our friendly teams at St Kitts Vets are here with urgent advice, rapid treatment and ongoing support whenever your pet needs us. Contact your nearest practice:

St Kitts Vets Hartley Wintney: 01252 844044
St Kitts Vets Basingstoke: 01256 844944
Crookham Park Veterinary Centre: 01252 913990
Firgrove Veterinary Centre: 01252 877799