Dog walkers are being warned against letting their pets go into rivers and ponds because of the risk of a potentially lethal algae.

Otter Vets, which has branches in Sidmouth and Ottery St Mary, said the blue-green algae releases dangerous toxins that a dog might ingest by drinking the water, or cleaning its fur after swimming.

The vets initially publicised the warning after the very hot spell at the end of May, as the bacteria tend to form in warm, dry conditions.

But veterinary surgeon Rebecca Tedford said the risk is not over.

She said: “We haven’t had any confirmed cases, but it’s something we’re still advising people to be aware of.”

The symptoms include vomiting, diarrhoea, seizures/fitting, weakness/collapse/unconsciousness, disorientation, drooling and breathing difficulties.

Any owner whose dog displays any of these symptoms after entering a river should get veterinary advice.

The bacteria can also cause rashes, sickness, stomach pains, fever and headaches in humans, with children at more risk than adults.