The spill, which began at Felixstowe Harbour and spread to Harwich at the weekend, came from a leak in a pipeline.

The oiled birds are being cleaned up at the RSPCA's wildlife hospital at East Winch in Norfolk.

The intricate work of cleaning the swans is very time-consuming. It takes an hour to bath each bird.

Staff at the hospital do not know exactly what kind of oil it is, but without thorough cleaning, the birds would no longer be waterproof, and could die.

The swans will spend around a week at the hospital to make sure they are fully fit before being returned to the wild.