The man was spotted by witnesses struggling to keep afloat in the water after he had rented a pedal boat at Regueral beach in the town of Cambrils on Sunday.
Emergency services were alerted but it was other beachgoers who initially pulled the man out of the water. By that stage he was in an unconscious state, online daily El Confidencial reported.
Upon arrival, the medical team performed CPR on the 31 year old but were unable to resuscitate him.
The possible reasons why the man fell off his rented pedal boat remain unknown.
Lifeguards at Regueral beach had hoisted the green flag at the time, meaning it was safe to swim.
Last May, a five-year-old girl died at the nearby Pineda beach after the inflatable donut she was on was dragged out to sea.
Spain’s Civil Protection unit has warned beachgoers “to be vigilant, to choose beaches whenever possible that are manned by lifeguards and to respect the safety flag (green: swimming allowed, yellow: lots of caution, red: swimming not allowed).