1 August 2014 Last updated at 13:50
More than 130 birds have died from avian botulism in parks across Merseyside, Greater Manchester and Staffordshire, the RSPCA has said.
RSPCA officers have found the bodies of swans, Canada geese, coots and ducks and have collected about 30 dead birds from Birkenhead Park in Merseyside.
The RSPCA is rescuing and treating birds that have contracted the disease.
Humans are not thought to be in danger, as the disease cannot be spread by touching or being near infected birds.
Avian botulism is caused by a water-soluble toxin produced by the bacterium Clostridium botulinum and is more often seen in warmer weather.
The RSPCA said the disease had affected birds at Newsham Park, Stanley Park and Walton Hall Park all in Liverpool, Boggart Hole Clough in Manchester, Rudyard Lakes in Rudyard, Staffordshire and Firs Park in Leigh, Wigan.