The Environment Agency is appealing for help to trace the cause of an oil leak on the River Wharfe.
A large slick of some kind of oil could be seen flowing through the middle of Otley last Thursday.
Robin Jakeways, of Whiteley Croft Road, spotted the pollution in the morning and, fearful of its likely impact on local wildlife, immediately contacted the authorities.
Mr Jakeways, who took this dramatic shot of the spillage from Otley Bridge, said: “The film of oil smells very unpleasant and is probably diesel.
“There are many birds on the river at this point and it is to be hoped that they will not be seriously harmed.”
An Environment Agency spokesman said: “We have received reports from members of the public regarding oil pollution on the River Wharfe by Otley Bridge, Otley.
“Environment officers are working with Yorkshire Water to investigate. There are no reports of wildlife in distress.
“Anyone who has any information about this or any future pollution incidents is urged to call the Environment Agency’s Incident Hotline on 0800 807060.”