A mysterious yellow and white substance washing up on Fylde coast beaches could be toxic palm oil, it is feared.
Pet owners have been urged to keep their animals away from the chunks, which have been removed from the sand at Knott End, Cleveleys, Fleetwood, and Lytham.
There are also reports of the substance washing up along the coast in Wales and Cumbria in recent days.
Coastguard workers said it is 'likely' to be palm oil, which can prove fatal to dogs who lick or eat it, but are now awaiting test results.
The Environment Agency has been drafted in to help investigate the incident, which is being treated seriously by council officials in Wyre.
The bathing water and beaches remain open, unlike earlier this year when they were closed after oil spilled from a storage tanker off the coast of Liverpool began washing ashore.
Fleetwood Coastguard tweeted this morning: "Please be careful when walking dogs on the beach until this substance has been identified."
And station officer Mark Sumner said: "If it turns out to be harmless, great, but if it's palm oil dogs could end up very ill, and death is a possibility."
Staff on routine patrol were diverted to clear around 50kg of the substance off the beach in Wyre over the weekend, he added, while Paul Little, station officer at Lytham Coastguard, said a large chunk was collected for sampling from the sand at St Annes shortly after high tide yesterday.
He said the substance, which is dense and smells like diesel, 'ticks all the boxes' of being palm oil, a waxy substance used in a variety of products and attractive to dogs.
It poses no threat to human health.
In March, Anglesey Council said palm oil that washed up near Trearddur Bay, on the north west tip of Wales, may have come from a ship that capsized 26 years ago, killing 10 crew members.
The Daily Post said recent storms are believed to have moved the wrecked Maltese vessel, Kimya, which sank 16 miles south west of Holyhead in 1991, and dislodged the oil.
And after oil was spotted near Trearddur Bay again last week, Mr Little said it is a 'possibility' that the same batch of oil has drifted up to the Fylde coast.
Blackpool Council said it has received no reports of the substance washing up on its beaches.
The Environment Agency said it is 'aware of a substance which has been washed up on the Lancashire and south Cumbria coast line'.
"Tests are being carried out to identify the substance, and partners from the Marine and Coastguard Agency are gathering information on the location and quantity," a spokeswoman said.
“We have received reports of an unknown substance washed up on beaches between Knott End, Fleetwood and Cleveleys yesterday (Sunday)," Wyre Council said.
"The substance can be described as fatty, oily, greasy with a rancid aroma and bright orange in colour.
"Our rangers are patrolling the beaches to monitor the situation and provide updates regularly.
"The beaches remain open, but we advise supervise children carefully and keep your dog on a lead.
"Please avoid all contact with residue on the beach and in the water due to potential health risks.”