Pet owners are being warned to avoid lakes containing toxic blue-green algae, as four dogs die after going for a swim.
The foamy substance known as cyanobacteria, found in lakes and rivers,can be fatal if bathed in or drank - causing breathing problems, fits, brain damage and liver failure.
Four distraught dog owners in Sussex, Cheshire, Edinburgh and Northern Irelandhave been left heartbroken after their pets died hours after swimming in water contaminated with the deadly algae.
The British Veterinary Association (BVA) is now warning owners to keep their dogs on leads around potentially infected waters.
It says there has been an increase in reports across the UK, including in Southampton, Cornwall, Derbyshire and Lincolnshire.
Particularly hot weather this summer is believed to have contributed to the outbreak, as long periods of warm temperatures can encourage algae to multiply and form blooms.
Cyanobacteria, a type of blooming algae, can produce toxins harmful to both humans and animals.
Though not all blooming algae contains cyanobacteria, dog owners will not be able ascertain this just by looking at the water.
Daniella Dos Santos, junior vice president of the BVA, said"While not all blue green algae are poisonous, it is impossible to tell the difference visually, so it is better to be safe than sorry.
"There is currently no known antidote for the toxins, so prompt veterinary treatment is essential to tackle their effects and ensure a good chance of recovery.
"If you suspect your dog has been exposed to blue green algae, rush it to your local vet without delay."