Coastguard crews stood down a search and rescue operation after a half hour operation found no-one in the sea between Central and South Piers, Blackpool.
Emergency services were alerted at 8.53am on Thursday to reports of a woman in the water, opposite the Lyndene Hotel on the Promenade.
Two coastguard boats were launched but an extensive search found nothing.
A spokesman for the coastguard said: “The initial report was of a person in the water, however the area has been searched with nothing found.
“We think it was probably a false alert with good intent.”
Police and ambulance were also at the scene but the search was stood down at 9.25am.
A spokesman for Lancashire Police said: “Witnesses said they saw a female in the sea.”