An investigation has been launched to trace the origins of an oil leak affecting the River Teifi in Ceredigion.
Environment Agency Wales said the leak had come from a pipe near a road bridge in Cardigan.
Officials leading the inquiry said it had not been possible to trace the source, although they claim it could be on an industrial estate.
The agency is appealing for businesses and residents to check for leaks.
Adam Thompson, who is leading the investigation for the agency, said: "We are concerned about this leak.
"It isn't necessarily causing serious environmental damage, but it is not pleasant for local people or for the wildlife there.
"Our main priority is to find out where it is coming from and stopping it at source.
"What we now need is the help of local businesses and residents to check if there is any leaking oil entering a surface water drain on their property and to let us know so we can help."
People with information can call an agency officer in Cardigan on 0800 80 70 60.