TESTS are being carried out by a leading animal charity after the deaths of more than 20 swans on a North-East river.

The birds have died on a stretch of the River Wear at Chester-le-Street, in County Durham, which flows through the Riverside Park, close to the Durham Emirates International Cricket Ground, home of County Cricket Club.

At the moments the deaths are a mystery and it is not known if they have been caused deliberately, accidentally, or are down to an illness.

Tests are being carried out on the birds by the RSPCA, which is urging visitors to the popular recreation area to watch out for other swans in distress.

About 100 swans live on that stretch of the river, which is a popular visitor attraction where people feed bread to the birds.

A sign was put up some time ago on the Riverside asking people not to feed the birds with mouldy bread as it is poisonous to them.

RSPCA Chief Inspector Michelle Charlton said: "Just over 20 swans have been found dead, or so sick that they've had to be put to sleep, on the river in Chester-le- Street over the past few weeks.

"Calls started coming in about them in January and RSPCA officers have picked several up over the past few days.

"Tests are being conducted on the birds but at the moment we have no idea what the cause is, whether it's the result of a deliberate act or a naturally occurring illness.

"Obviously we are very concerned about this and are working with The Swan Trust, vet practices Cestria Vets and Robson & Prescott Vets in Morpeth, Defra, the environment agency and the police to try to find out what the cause is.”

Insp Charlton added: "We'd like to appeal to the public to be vigilant, and if you come across anything that you think might be being dumped into the water to contact us."

Anyone who sees a swan, or other bird or animal in distress, can call the RSPCA for help and advice on 0300-123-4999.