Rescue crews spent 90 minutes searching the sea after a report of a person struggling in the water, only to find an inflatable doll.
Around 40 people were involved in the air and sea search when the alarm was raised in Newquay, Cornwall, on Monday.
An angler had dialled 999 to report a person in the water just north of the harbour.
The doll was recovered from Newquay Bay by the RNLI after they joined a coastguard helicopter in the search.
Gareth Horner, lifeboat operations manager for Newquay RNLI, said search conditions at that time of night were "uncomfortable" with a large swell.
"It was good information from a reliable source known to us and he was quite certain that it wasn't a seal or anything like that," he said.
"An inflatable doll is very light, it scoots across the surface of the water, so it was some way from where we started our search."
The doll was dressed in trousers and T-shirt.
"We would hope it got into the sea accidentally," he said.
Mr Horner added: "The 999 caller gave accurate information which led to a successful search and a positive outcome.
"If you think you see somebody in difficulties at sea, do not hesitate, please call 999 and ask for the coastguard.
"While the doll may have been deflated by the incident we were happy to discover no-one was hurt."