The cause of the two mile oil slick that saw more than 70 swans rescued from the Thames remains a mystery.
Volunteers spent three days retrieving swans from a two mile stretch of the river at Windsor, after the oil slick was spotted on Monday.
The swans had to be cleaned at the sanctuary in Eton, before the oil saturating their feathers could do permanant damage.
The oil finally cleared after three days, after Environment Agency staff laid special 'booms' across the river to stop it spreading.
Samples have been taken and sent for analysis but it will be next week before results come though, giving the EA team a chance of identifying the source of the leak.
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Trains travelling to and from London Paddington are facing 'major disruption' this afternoon, with some services set to be delayed by up to an hour, cancelled or revised.