Although contained quickly, the spill on Friday morning caused huge problems for wildlife and many sea birds had to be rescued.

So far 28 swans have been recovered and taken to East Winch Wildlife Centre, near King's Lynn, Norfolk, to have their feathers cleaned.

RSPCA officers are combing the area for more birds.

Inquiry into the spill

RSPCA spokeswoman Ann Grain said it was impossible to say how many birds had been affected.

"It mainly seems to be swans. Ducks and sea gulls do not seem to be affected as badly.

"The rescue operation will go on until we feel we have recovered all the swans", she said.

An investigation has been launched at the dock to find out what caused the spill.