The Scottish SPCA has been caring for a male adult swan, which was carefully cleaned after coming into contact with a spill at Stenton Pond in Glenrothes, Fife.
A concerned member of the public called the SPCA after coming across the injured bird.
Colin Seddon, manager of the National Wildlife Rescue Centre at Fishcross, near Alloa, said: "From the pattern of coverage it would appear that the swan had dipped his head and neck into a diesel oil spill, which had possibly gathered in reeds at the edge of the pond.
"It is not uncommon for waterfowl to come into our care in this state, often as a result of people irresponsibly disposing of oil in ponds and waterways.
"This is a very reckless and dangerous thing to do as diesel is an irritant, which can cause extreme burning to the skin.
"Birds can and do die from the injuries they sustain from this type of oil so we'd strongly urge people to dispose of this material in a responsible manner."
Mr Seddon added: "Thankfully we were able to clean and treat the swan before it was too late, although he has lost a lot of neck feathers due to the burning effect of the oil and he was underweight on arrival, suggesting he may have swallowed some of the diesel too."