Five swans covered in diesel were rescued from a lake by the RSPCA after a suspected pollution incident.
A specialist water rescue team was drafted in and captured them to be cleaned.
All five swans are expected to be returned to the wild diesel-free soon after treatment at a wildlife sanctuary.
The RSPCA said it received reports of what was described as a diesel spillage at fishing lakes off Scot Lane in Martland Mill, Wigan, on Wednesday.
Officers used a water rescue boat to locate then capture the affected swans.
They were taken to the charity's Stapeley Grange Wildlife Centre in Nantwich, Cheshire, where the time-consuming task of cleaning their plumage has now started.
If oil isn't removed quickly from waterbirds it reduces the natural waterproofing in their plumage, leaving them at risk of dying from hypothermia.
The RSPCA said it was vital the swans were treated as soon as possible.
RSPCA Animal Welfare Officer Jonathan Brooks said: "We received a call that some swans appeared to be covered in oil from a spillage and I attended the scene.
"It was dark but I could see five swans on the lake which were contaminated with oil.
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"We had a team of officers at the lake with a water rescue boat to capture the affected swans and we managed to get all five safely.
"Pollution on the feathers damages the structure of them and also when they are preening, they can ingest the contaminants and this makes them ill.
"When they are preening they are not eating so lose weight and become weak.
"With the feathers not protecting them they can also become hypothermic as they can’t keep dry and warm so we will have fatalities if we don’t intervene, which is why we have to act fast.
"They will be taken to our wildlife centre where staff will clean the birds carefully with washing up liquid and once they have recovered they will be returned to the wild."
The RSPCA said the cause of the pollution was not yet known.
They said the Environment Agency were aware and had launched an investigation.
