Initial press reports claimed that a shark had approached the Moll Grec beach in Sant Martí d'Empúries on Catalonia's Costa Brava.
Red Cross lifeguards warned bathers to beat a retreat to the sand at 5.30pm on Tuesday when a man claimed minor injuries on his arm had been caused by a blue shark (Prionace glauca).
Five beaches were closed and red warning flags were raised.
A search ensued but there was no trace of the animal, according to Catalan daily El Periodico.
None the people who claimed to have seen the shark were able to provide any corroborating details.
After examining the injured man's arm, doctors ruled out the possibility that it had been caused by a shark and the incident was dismissed as a false alarm.
The Mayor of L'Escala blamed the rumour on "nervousness".
The blue shark is commonly found off the coast of every continent but there have only ever been 13 recorded blue shark attacks on humans, leading to just four fatalities.