Blue-green algae: a hidden summer danger for dogs
Blue-green algae is a serious threat to dogs during warm weather, and Rachel Garbutt, Registered Veterinary Nurse at Butternut Box, highlights what owners need to know. With her years of clinical experience and expertise in pet health, Rachel explains how to recognise the presence of blue-green algae, understand the risks it poses, and take practical steps to protect dogs from potentially fatal exposure.
Blue-green algae are something dog owners should take seriously. Despite the name, it’s not actually algae but a group of bacteria known as cyanobacteria. When these bacteria clump together, they can look like algae and form blooms in still or slow-moving bodies of fresh water, especially during warm weather and dry spells.
You might spot it as green flakes, brown dots, or scum sitting on the surface of a pond or lake. In full bloom, it can give water the look of pea soup or create foam-like build-ups around the edges. While it’s more common in summer, blue-green algae can appear at other times of year, too.
Why Blue-Green Algae is So Dangerous
The real issue is that some types of blue-green algae produce toxins that are highly dangerous to dogs. These toxins can cause liver failure and, in the most severe cases, can be fatal within an hour of exposure. Dogs are at risk if they drink contaminated water or even just swim in it — the algae can stick to their fur and be ingested later when they groom themselves.
What makes things more complicated is that it’s impossible to tell whether a bloom is toxic just by looking. And not all affected water looks suspicious — toxins can still be present even if the surface looks clear. That’s why the best approach is to avoid letting your dog swim in or drink from still water during high-risk periods, and always pay attention to any local warning signs.
Spotting the Signs and Acting Fast
If a dog has been in or near water and starts showing symptoms such as vomiting, diarrhoea, drooling, disorientation, breathing difficulties, seizures, or sudden weakness, it’s critical to get them to a vet immediately and mention the possibility of blue-green algae exposure. There’s no antidote for the toxins, but if caught early, vets may be able to treat the effects before they become life-threatening.
To stay safe, avoid lakes and ponds where blue-green algae could be present, especially during warm, dry weather. Don’t let dogs drink from or paddle in water that looks greenish, foamy, or scummy, particularly around the edges, where toxin levels can be higher. When in doubt, steer clear. The health risks are too serious to take chances. A cautious walk and a bowl of fresh water are always better than a dip that could end in a vet emergency.
The Bowl Slime Myth: Not the Same as Blue-Green Algae
If you’ve noticed green slime forming in your dog’s water bowl, don’t worry — this isn’t the same as the dangerous blue-green algae (cyanobacteria) found in lakes and ponds. The residue in bowls is usually a harmless biofilm made up of water-loving bacteria, algae, fungi, and other microorganisms. While not toxic like blue-green algae, if left uncleaned, it can become a breeding ground for harmful bacteria such as E. coli or Salmonella, potentially causing stomach upsets or infections in dogs.
On the other hand, blue-green algae are a type of bacteria that can release potent toxins which affect the liver and nervous system, and can be deadly if ingested or licked from contaminated fur. They typically bloom in warm, stagnant freshwater during dry, hot spells. Regular cleaning of your dog’s bowl with hot, soapy water can prevent biofilm buildup and help keep your dog’s drinking water fresh and safe.
