Red flags were raised at the Arenales del Sol beach in Elche on the southeastern Mediterranean coast of Spain after the attack.
Lifeguards said that the man, a resident of Elche in his forties, emerged from the sea with blood coming from his hand after he was bitten by what is thought to have been a shark.
“It was a serious bite,” a spokesman at the DYA ambulance service told local media, confirming that the man was taken to hospital for stitches.
“We had to raise the red flag and call all of the swimmers out of the water,” the spokesman said.
According to Spanish news agency Efe, the most likely culprit was a Blue Shark, (Prionace glauca) which can typically grow to between 1.8 and 3.4 metres. They usually prey on squid and small fish and do not typically attack humans.
Last summer a shark caused panic on the beach up the coast in Benidorm after a boy was bitten on the torso.