Lifeboat volunteers in Blackpool battled to save the life of a woman in the water, the RNLI said.
Both the resort's class D lifeboats launched at around 2.30pm after a 999 caller said they had lost sight of her, it is understood.
The casualty was brought to shore, an RNLI spokeswoman said, and was given first aid at the lifeboat station on the Promenade.
The air ambulance landed close to Central Pier, she added.
Police said officers were called out by the Coastguard to reports of a woman in the water near to the lifeboat station.
She is understood to have been taken to Blackpool Victoria Hospital, a spokeswoman for Lancashire Police said.
An ambulance service spokeswoman said the helicopter was not needed, with the woman taken to hospital via road.
She is understood to be in a critical condition.