Garden and pest control
Is blue-green algae toxic to cats and dogs?
Also sold as cyanobacteria, algal bloom, toxic algae, pond scum
Cats
Highly toxicDogs
Highly toxicSome blooms of blue-green algae in lakes, ponds and slow rivers produce toxins that can kill a dog within hours. Dogs are exposed by swimming, drinking the water or licking their coat afterwards.
By Maya HartIf your pet got into it
- Rinse your dog thoroughly with clean water, wearing gloves, and go to a vet straight away — nerve toxins can act within minutes.
- There is no antidote, so early treatment matters.
Signs to watch for
- Vomiting and diarrhoea
- Drooling, trembling and muscle twitching
- Weakness and wobbliness
- Breathing difficulty
- Seizures and collapse
- Pale or yellow gums (liver damage)
How much is dangerous
Small amounts of water from a toxic bloom can be fatal. You can’t tell whether a bloom is toxic by looking at it.
Keeping it safe
- Keep dogs out of water that looks green, scummy, like pea soup or spilled paint
- Obey warning signs at lakes and reservoirs
- Be extra careful in warm, still weather in summer and early autumn
- Carry fresh water for your dog
- Rinse your dog after swimming in natural water
The details
Algal blooms form when warm, sunny weather and nutrients from fertiliser run-off let cyanobacteria multiply. Not all blooms are toxic, and toxic ones can look identical to harmless ones — so the only safe approach is to keep dogs out of water where a bloom is visible. Dogs are at far higher risk than people because they swim, drink and then groom.
Algae can also collect along the shore, where wind blows it into mats, and dried mats remain toxic.
Questions owners ask
Is blue-green algae toxic to cats?
Yes — highly toxic.
Is blue-green algae toxic to dogs?
Yes — highly toxic.
How much is dangerous?
Small amounts of water from a toxic bloom can be fatal. You can’t tell whether a bloom is toxic by looking at it.
What should I do if my pet got into it?
Rinse your dog thoroughly with clean water, wearing gloves, and go to a vet straight away — nerve toxins can act within minutes. There is no antidote, so early treatment matters.
Sources
Tailwise is for general information and is reviewed by veterinary professionals, but it is not a substitute for advice from your own vet, who knows your pet. How we check facts