A 14-year-old girl who died when on a training expedition on Dartmoor, saw her friends cross a river before she was swept away.
Three school teams were airlifted after heavy rain
Charlotte Shaw, from the Torrington area in Devon, was in a party of 10 from Edgehill College who were training for the Ten Tors Challenge.
The event sees thousands of youngsters walk on courses across the moor.
A police spokesman said all her group were across the rain-swollen Walla Brook, before she crossed.
Miss Shaw somehow ended up in the water and help was summoned by one of her group on a mobile phone.
She was airlifted to Derriford Hospital in Plymouth, but died early on Monday morning.
Twenty-six people from three schools, including Edgehill, were airlifted from the moor in atrocious weather.
Devon and Cornwall Police are investigating the incident, which happened at about 1405 GMT on Sunday, and the coroner's office has been informed.
Members of the dead girl's team will be interviewed as part of the police investigation.
The college said in a statement: "We are all shocked by the tragedy and are working to support all the pupils and staff in coming to terms with what happened."
About 85 teams were training on the moor over the weekend.
The Army, which organises the Ten Tors event - now in its 47th year - has said there were no plans to cancel or change it.