Authorities made the decision to close the Fuengirola beach on Sunday afternoon when it was packed with tourists enjoying the last weekend in August.
Just after 12pm some bathers reported seeing what appeared to be a four-meter-long shark and alerted lifeguards.
The red flags were immediately raised and the Guardia Civil sent a patrol boat to search the stretch of coast for the fish.
But by 5pm and with no further sightings the beach was reopened for swimming.
Last month a swimmer was bitten by a small shark while swimming off a beach in Elche, Alicante.