Bathers at Barril beach, Tavira, were told to get out of the water - and quick - on Monday afternoon but only ‘as a precaution’ after a shark's fin was spotted, cutting through the shallow waters of the Ria Formosa.
Bathers contacted the on duty life guards who in turn alerted the Maritime Police but searches failed to locate the predator. The beach was full of holidaymakers and the red ‘no swimming’ flag was rapidly hoisted.
"The Maritime Police patrolled for two and a half hours in the sea along the beach, to see if they could find anything. They did not and the green flag was raised again," said Commander Cortes Lopes.
The fin did not necessarily have to be attached to a shark as other sea creatures have similar looking appendages. This can lead to confusion - and blind panic in faint-hearted swimmers.
The bathers gingerly got back into the sea for a final swim before wading ashore and heading home with all limbs still attached.