A British expedition leader was swept out to sea off South Africa after diving into the shark-infested water to help a group of schoolchildren in difficulty.
Sean Foxcroft, 24, from Manchester, was leading a team of 15 students aged between 16 and 18 on a four-week World Challenge trip.
A search was launched for the missing man but the South African authorities said he was "presumed to have drowned".
Mr Foxcroft was supervising the teenagers as they played rugby with another World Challenge group on the beach at St Lucia, north of Durban on South Africa's east coast.
Some of the students went into the shallow surf to cool off, but strong undercurrents dragged them out of their depth and they began to struggle.
Along with another expedition leader, Mr Foxcroft went into the water to help them but he was overwhelmed by the waves and carried out to sea.
The South African authorities launched a major sea, air and land search but failed to find him.
A spokesman for South Africa's National Sea Rescue Institute said today: "Shore patrols conducted during the night have revealed no signs of the missing man, who is presumed to have drowned."
World Challenge said the rescue mission was still ongoing.
The company said in a statement: "The team had been playing rugby on the beach when some of the team members entered the shallow surf to cool down but were swept out beyond their depth and began to struggle with the strong currents.
"Two expedition leaders went to provide assistance but although the team members made it back to the shore safely, one expedition leader was overwhelmed by the conditions and was carried out to sea."
Nobody else was hurt in the incident, World Challenge head of communications Chris Gallant said.
The students, accompanied by four teachers, had spent the past three-and-a-half weeks trekking in South Africa and were on the final wind-down phase of their trip.
They are due to return to the UK on Wednesday and in the meantime are receiving counselling for their ordeal.
World Challenge would not confirm their school, but said they were one of 317 UK school expedition teams travelling to a total of 40 destinations with the company this summer.