RSPCA officers have said they have spotted at least a dozen contaminated swans but expect the problem to get worse.

The diesel has leaked from a cabin cruiser in Brayford Pool which sunk in the early hours of Tuesday morning.

It is believed the vessel had been deliberately set on fire.

On New Year's Eve more than 60 swans had to be rescued from Brayford Pool after they became covered in oil from an unknown source.

The RSPCA only began returning those birds 10 days ago after they had been treated at a wildlife hospital in Norfolk.