A rescue operation is under way after 100 seabirds were washed up on the south coast covered in an unidentified sticky white substance.
The Royal Society for the Protection of Birds (RSPB) said the guillemots, a kind of awk, were discovered on Lyme Bay near Weymouth.
They have been taken to West Hatch Animal Centre in Taunton but attempts to clean them have been hampered by not knowing what the substance is, Grahame Madge, of the RSPB, said.
"At the moment, the best guess is there are around 100 birds ashore and there are concerns the birds are affected in as widespread a region as from Cornwall to Sussex so we could be dealing with quite a large incident as all these birds could be proved to come from the same pollution incident," he added.
"We are urging the Government to identify the source of the pollution and the pollutant."
The rescue operation is being run by the Royal Society for the Protection of Animals (RSPCA).
Mr Madge added: "The RSPCA are having difficulty with the clean up of the birds. With oil you know what it is and how to deal with it but the unidentified substance is hampering efforts."
The RSPCA said many of the birds, which were "mainly being found near Portland, west Dorset", had "very sore legs" but there was no number for how many had died.
Peter Venn, manager of RSPCA in West Hatch, Somerset, said: "The numbers of birds arriving in to our centre are growing and we are doing all we can to help them - but it is too early to tell how successful these attempts will be.
"We do not know what this substance is or where it has come from yet but we do know it is not fuel. It may be bi-product from manufacture, but at this stage we just do not know."