Investigators have drawn a blank in their attempts to pinpoint the source of the two mile oil slick that hit the Thames at Windsor.
The slick spread between Baths Island at Stovell Road and Romney Lock a fortnight ago before Environment Agency team managed to contain and dissipate it.
This week James Liney from the Environment Agency admitted the EA had been less successful in finding what caused it.
He said: "We have carried out an extensive search for the source of the oil but unfortunately have not been able to establish where it came from.
"There have not been any repeats of the incident during the past two weeks. We will be carrying out pollution prevention visits to the area in the coming weeks and months to explain to businesses the correct methods to dispose of waste oil to prevent a repeat of this sort of incident."
The rescued swans have all been returned to the river by Swan Lifeline.
Top Ten Articles
It's time to get voting as readers get their chance to decide the winner of the Independent Retailer of the Year at the inaugural Windsor and Maidenhead Business Awards.
A woman was declared dead in the early hours of this morning (Tuesday) after being pulled out of the water at the Racecourse Marina in Windsor.