LONDON, Aug. 6 (Xinhua) -- Dozens of swans and geese have died in London in an outbreak of avian botulism caused by the heatwave, local press reports said on Monday.

The Swan Sanctuary in Shepperton is caring for around 300 water birds, many suffering from the deadly illness and most rescued from ponds and lakes in the British capital. Shepperton is some 25 km southwest of central London.

The extreme heat means there is less oxygen in water, providing the perfect breeding ground for the botulin toxin.

Affected birds are unable to use their legs or fly, and their neck muscles can be paralyzed. They commonly die from respiratory failure or drowning.

Dorothy Beeston, founder of the Swan Sanctuary, told the Evening Standard, a London-based newspaper, "In the last three or four weeks we have seen a huge spike in the number of birds being brought into the hospital with botulism."

"It's been dozens of calls a week, which is just terrible," Beeston said. "Hot weather often causes an outbreak but this is one of the worst I've seen in the 39 years we have been set up."