A young man's family watched in horror as he "tried to keep his head above water" before he died in a jet skiing accident.
The 26-year-old man died after he became separated from his jet ski at Goring-by-Sea, near Worthing, shortly before 6pm on Bank Holiday Monday.
Eyewitnesses said he was too far out from shore as lifeboat rescuers scrambled in vain to save his life.
He had been enjoying a day on the water with his family, who were on the shore at the time of the tragedy. His family could only watch on as he struggled.
Eyewitness Tracy Thompson told of her shock at seeing the young man struggling to keep his head above water.
A keen sea swimmer, Tracy said offshore wind, fast current and water temperature would all have been factors.
She said: "I didn't see him come off of it, just saw him in the water. The current was strong and took the jet ski too far away from him.
"It was far, far away when I saw him and realised that he wouldn't get to it or be able to swim to the shore.
"He was trying to keep above the water but kept disappearing.
"It was a very strong offshore wind which takes you away from the shore, so I knew he was not going to get back.
"One of our group used his phone to call it in. Heartbreaking watching him while helpless on the shore.
"So sad, so young. He was only having fun.
"The sea can be so cruel, even with a wetsuit and life jacket it still wasn't enough for him. Tragic."
When emergency services reached him, he was alive, but an ambulance service spokesman said he was taken to hospital in a life-threatening condition where he later died.
Thousands had flocked to the south coast as temperatures peaked at 22C, making the Bank Holiday weekend the hottest of the year so far.
A spokesman for Sussex Police said: "Emergency services responded to a report of a medical incident in the sea at Worthing Beach, shortly before 6pm on Monday, May 29.
"A 26-year-old man was taken to hospital, where sadly he was later declared deceased.
"His next of kin have been informed."
A spokesman for the Coastguard said: "HM Coastguard, Sussex Police, South East Ambulance Service and an air ambulance responded to reports of a man separated from his jet ski off Goring-by-Sea.
"At around 6pm a Coastguard Rescue Team from Littlehampton and a lifeboat from Littlehampton RNLI were sent to the scene."
The RNLI said: "We can confirm that Littlehampton RNLI was paged and launched the charity's inshore Atlantic 85 lifeboat at 5.55pm on Sunday."
A report will be prepared for the coroner, police said.
