Over 22 swans and other birds have been forced to wade through oil dumped in the River Welland.
Devastating pictures have emerged from Deeping Lakes, which show how swans are covered up to their necks in what is believed to be waste engine oil.
The Environment Agency found five 25 litre oil drums in the river when they were called, thought to have been dumped into the river from the bridge in Peakirk.
Lincolnshire Wildlife Trust posted the pictures along with a statement: “We did try rounding up a flock of around 20 swans yesterday, they took off and flew away.
“Trying to round up birds that are still capable of flight is not easy, and if they fly off and disperse we will never catch them.
“The truth is that someone knowingly dumped the drums in the river and the result is likely to be considerable damaged to the wildlife.”
Lots of people were furious and commented on the post to call for those responsible to be made to clean the river.
Gavin Smith said: “It’s so horrible that someone would do that, why throw them in the river which would kill fish and a whole array of other animals when you could just of left them by the side of the road?
“I know that’s not what you should do with them but better that than kill innocent animals.”
While Barbara Piercy wrote: “The person or persons who carried out such a thoughtless act need to be tracked down and made to help clean the poor wildlife they have tried to destroy.
“There has to be other animals damaged or killed besides the swans. I find it so sad that someone would do that to such beautiful creatures.”
They have installed a boom to collect oil near Crowland, meaning that there could be over seven kilometres of polluted water.
Experts anticipate that more sick and distressed birds will emerge over the next few days.
Any birds showing signs of sickness should be reported to the RSPCA on 0300 1234999.