PET owners have been warned to be ‘extra vigilant’ following the death of two dogs which had swum in Windermere.

The sudden deaths have raised fears that a potentially toxic algae may be polluting the water.

Vet Steve Dodwell raised the alarm about blue green algae forming on the surface following the deaths of the dogs.

Four-year-old greyhound Jem had been paddling during a walk close to Borrans Road, near Ambleside, with his owner John Pratt.

“He just collapsed outside the Co-op (in Ambleside). One minute he was fine and the next he couldn’t stand,” said Mr Pratt.

“I had to call my partner to bring the car so we could take him to the vets.”

Mr Dodwell, of Oakhill Veterinary Centre, was unsuccessful in his attempt to save the dog. He fears blue green algae could be behind its sudden death.

Mr Dodwell has also treated a lurcher that died after going into the lake.

“Based on clinical appearance and the circumstances surrounding the deaths it would seem that algae was behind the deaths,” he said.

“But there are no specific tests available to prove for certain.

“I would warn all dog walkers to be extra vigilant when around the water’s edge. I don’t want any more animals to die unnecessarily.”

Lake wardens are on high alert for signs of the deadly algae.

Warden Trabis Spriskie said: “If we do see any blooms we will put up warning signs and warn people who are around the water about the risks.

“I would advise dog walkers and swimmers, if the water does look unclean then don’t go in.

“Algae can cause rashes or flu-like symptons if humans have contact with it”

Hugh Lamont, from Health Protection North West, said blue green algae could cause diarrhoea, sickness, severe rashes, dizziness and vomiting.

“If it is present in the water it is essential not to go in,” he said.

The Environment Agency has tested the water but has only found low levels of algae.

Graham Miller, Environment Agency Team Leader, said: “Blue-green algae and other algal groups are present in inland waters, estuaries and the sea.

“A bloom sometimes forms when their numbers become excessive - this can often happen during periods of warm, calm weather.

“Some types of algae blooms produce toxins that can be dangerous to animals and humans.

"We have tested the water in Windermere and although a low level of algae was present in the sample, there was not enough to pose a danger to water users.

“The Environment Agency regularly monitors water quality and if a sample shows a high level of algae, we immediately notify the local authority and owners of the waterbody, so they can take appropriate steps.”

Richard Green, owner of the Waterhead Coffee shop, Ambleside, said: “I saw a green film on the lake’s surface last week. You can see it when it gets really hot.”

If anyone spots an algal bloom that call the Environment Agency’s incident hotline 0800 80 70 60."