Lifeguards pulled a swimmer from the sea in Hove after he was spotted face down in the water but they were unable to save him.
The man, reported to be in his sixties, was brought ashore near the King Alfred Leisure Centre just after 2pm on Friday (20 June).
Efforts to revive him were made by the Brighton and Hove City Council lifeguards.
The RNLI in Brighton tweeted yesterday (Saturday 21 June): “Yesterday’s service was to a person face down in the water at King Alfred. Once on scene the lifeguards had recovered the person and CPR was started until @SECAmbulance arrived to take the casualty to hospital. The lifeboat remained on scene to give assistance.”