More than 20 distressed swans in the River Welland have been left covered in oil after the toxic substance was dumped into the water.
A dog walker discovered the distressing scene near Deeping Lakes in Deeping St James yesterday morning (Tuesday).
The Environment Agency and RSPCA were called to the site, with the EA finding five 25 litre oil drums thought to have been dumped from the bridge in Peakirk.
The EA installed an oil boom (high strength floating barrier) to collect what is believed to be waste engine oil.
Lincolnshire Wildlife Trust, which revealed the oil dumping, said there was more than 7km of polluted river, with at least 22 oiled swans.
The stretch of affected river runs between Peakirk and Crowland.
The wildlife trust said: “The EA and the RSPCA will be monitoring the situation - it is anticipated that sick/distressed birds will become more noticeable over the next few days.
“Any birds showing obvious signs of being unwell should be reported to the RSPCA on 0300 1234999.”
According to the Swan Lifeline charity, if the swan tries to clean itself and ingests the oil it will poison them and can be fatal.
The oil also causes swans to lose their waterproofing on their feathers which can cause difficulty being on water.
The Peterborough Telegraph has contacted the Environment Agency for comment.