Beaches in part of Kent remain closed as a major clean-up operation continues following the discovery of oil deposits along the coastline.
Thanet District Council said a "significant" amount of oil was found on 18 beaches on Wednesday, prompting widespread closures.
Clean-up crews began work on Thursday, with residents, especially dog owners, being urged to avoid the affected areas.
Mike Humber, the council's director for the environment, said the operation would "take several days" but could not provide a timescale for reopening.
He told BBC Radio Kent that contractors were on site using specialist equipment to remove the oil and were cleaning up as quickly and carefully as possible.
"The tide comes in and out twice a day and we have to continue to assess and determine see where the oil is, and deploy resources where it's most needed," he said.
He explained the weather could affect the spread of the oil droplets.
"[On Thursday] we had strong winds and it blows the sand across the oil and makes it more difficult to spot."
A council spokesperson said its coastal engineering team was working with the Maritime & Coastguard Agency (MCA) and specialist contractors to locate and remove the oily deposits.
The situation has been reported to the Environment Agency.
The council says the source of the oil "remains unknown" and samples have been collected and sent for analysis.
A spokesperson for MCA said coastguard officers from Margate, Herne Bay and Deal had conducted observation patrols.
"An overflight by HM Coastguard on Thursday was unable to identify any source of pollution," they said.
"Shoreline clean-up remains the responsibility of the local authority or landowner."
Warning signs remain in place at beaches from Minnis Bay in Birchington to Ramsgate Main Sands.
Follow BBC Kent on Facebook, external, X, external, and on Instagram, external and listen to BBC Radio Kent on Sounds. Send your story ideas to southeasttoday@bbc.co.uk, external or WhatsApp us on 08081 002250.
More coverage
Oil spill closes 18 beaches across Kent
‘It’s been amazing’ – Owain Wyn Evans completes four-nation Children in Need ride
Man arrested after woman, 80, set on fire
Discussion