A woman had first waded in and tried to help the mammal, which was spotted in trouble on the shore in Birkdale, Merseyside, on Tuesday afternoon.
Volunteers from Southport Lifeboat then managed to free the porpoise with help from British Divers Marine Life Rescue.
Staff held the 5ft (1.5m) adult until it had recovered enough energy to swim safely back to deeper waters.
Senior coxswain Keith Porter said the porpoise was found in a “distressed” state.
He added: “It had been rolling about in the surf and was trembling with exhaustion.
“We were able to hold it until it recovered enough strength to swim back into deep water.”
Mr Porter, who has worked on lifeboats for 31 years, said although porpoises are common off the Sefton coast he had never seen one so close to the beach.
Staff remained at the scene for several hours to ensure that the animal did not return to the shore.
Source: BBC
