Specialists working to clear up oil that has washed up on beaches along the Fylde coast suspect it came from a ship.
Samples of the black tar-like substance has been sent to Edinburgh for testing, with results that will give a more definite answer expected back tomorrow.
A spokeswoman for the Maritime and Coastguard Agency said: "There was an incident that resulted in the release of crude oil from a ship, more than 30 kilometres from the coast of north west England on Monday, July 10.
"We believe that the oil is from that incident, but until we have confirmation from the test results we cannot say for certain.
"The incident is relatively contained and Braemar are on scene leading with the clean-up operation.
"Locally, the local authorities are requesting that members of the public stay safe by staying well away from the area until the clean-up operation is complete.”
It is not yet known whether the release was accidental or deliberate, but as decontamination units and beach workers fight to clear miles of coastline of the spill, fears have been voiced for the Irish Sea’s thriving marine life.
A number of dead birds were spotted among washed-up seaweeds by one dog walker, said to be cormorants by another man, while a dead porpoise was also investigated by the Coastguard.
That was found to be badly decomposed and not a victim of the spill, while no wildlife has been reported washed up, the Coastguard service said, but former animal lecturer at Myerscough College John Vale said: “It could affect the whole ecosystem. Any spill is too big.”
Mr Vale, who lives in Blackpool, said the oil could kill off basic microscopic life, which in turn could impact on larger marine animals.
But he warned wintering birds in the Wyre estuary could also be affected, and said: “Fortunately we have beaches you can get vehicles on and get rid of the oil.
“If it’s not, and it’s already flowing into the estuary, it could severely affect the winter population of birds.”
Clumps of black substance, which has left the sand reeking of fuel, began to wash up at Bispham at the weekend and has since been spotted as far south as North Pier, and as far north as Knott End.
The sea was ordered off limits at both Cleveleys and Bispham earlier today, while the Fleetwood to Knott End ferry service was also suspended because of the treacherous slipway.
Ferry skipper Tony Cowell said it was the first time he had ever experienced such a situation, and that he expects disruption tomorrow too.
“We just couldn’t operate the ferry for health and safety reasons," he said.
“There were globules of this oil type substance all over the slipway at both Fleetwood and Knott End and it was incredibly slippy and dangerous.
“There is no way we would put passengers at risk and we were advised by the Coastguard Agency to stop operating until further notice,
“We were also worried about getting this stuff on passengers;’ clothes, it’s horrible stuff. They’d never get it out.
“We’ve been given a high pressure spray to use on everything on Wednesday and were told not to think of operating until we’ve got the all clear.”
He said people in protective suits had been on Fleetwood beach and samples of the substance had been taken away.
He also said people had been on the beach early on today attempting a clean-up.
Those who may have already come into contact with the oil and tar-like spots have been urged to seek immediate medical advice should they start to feel unwell.
Posters were put up at Bispham warning of an ‘abnormal situation’, with people told not to bathe or paddle in the water there.
And A4-sized notices were also posted up at Wyre, including at Rossall beach, where there was no visible sign of a spill but a strong smell of fuel in the sand.
On Monday evening, it was still busy with dog walkers unaware of the pollution incident, while children were still playing on the beach at Cleveleys this morning, despite chunks of oil lying in the sand nearby.
Wyre Council said it was urging people to avoid contact with ‘any visible oil or tar on the beach and in the water, to supervise children carefully, and keep your dog on a lead’.
“The advice from Public Health England is that it is very unlikely that anyone exposed to crude oil for a short period of time will have any long term health effects,” it said in a statement.
“Short term exposure to skin may result in irritation so as a precaution members of the public are advised to avoid contact with the material.
“If you touch the tar balls and get oil on the skin, remove affected clothing and wash with soap and water for 10 minutes.
“If you feel unwell seek medical attention.”
Allan Wilkinson, 68, watched on as a decontamination unit arrived to clean up the beach and slipway at Knott End earlier.
He said a horde of people in fluroescent jackets were clearing solidified oil from the beach in clear bags, and said: “There’s notices up right along the front warning people about taking their dogs on the beach and taking their kids on; basically they are warning people to keep off.
“It’s worrying but it’s more annoying that we can’t go on the beach while it’s being cleaned up.”
Experts from Braemar Response, which has a history of working to clear up environmental disasters, have been drafted in, with council cleaning staff also being tasked with shovelling up affected sand.