A major clean-up operation is underway along a 15-mile stretch of coastline between Scarborough and Speeting after pools of oil washed up on beaches yesterday.
The substance has been found in South Bay, Cornelian Bay, Cayton Bay and Filey and the sizes of the deposits vary - with the largest being a the size of a plate.
A small number of dead seabirds have been found and surfers are being warned to stay out of the water until further notice.
The Maritime and Coastguard Agency, Scarborough Council and the Environment Agency have launched an investigation to try to establish where the spill has come from.
It is thought the oil, which washed up late yesterday afternoon and overnight, hit the shoreline as a result of the strong easterly winds and heavy sea conditions.
The Maritime and Coastguard Agency has carried out a surveillance flight, and together with the Environment Agency, is arranging for samples of the substance to be tested.
Andy Skelton, Scarborough Council’s head of environmental services said: “We would like to thank those surfers that notified the relevant agencies after seeing deposits of oil at Cayton Bay yesterday. We subsequently advised local surfing groups, the main beach users at this time of year, to stay out of the sea until further notice. We are also putting up warning signs at the beaches to advise the public of the problems.
“We have had reports of a small number of dead seabirds being found. Currently the number is thought to be no more than 15, but we are unable to assess what impact, if any, there may have been on the wider marine environment. We have ensured the RSPB and RSPCA are aware of the problem.
“We will continue our clean up operations during daylight hours today and will resume again at first light in the morning. We should be in a position to issue a further statement late tomorrow morning when we see whether anymore oil comes in on the overnight tide.”
A spokesman for the Maritime and Coastguard Agency, which monitors coastal water pollution, said: “We are working together to investigate reports of oil on the beach and in the water off the coast of Cayton Bay down to Filey.
“A counter pollution surveillance aircraft has carried out a search of the area, but no pollution was detected.
“Tests are now being carried out on a sample of the product to try to identify exactly what it is and if at all possible, to determine the source.”