The girl was seriously hurt when she fell into the water as torrential rain and heavy winds lashed the national park in Devon yesterday.
Her friends lost sight of her and called for help on a mobile phone. She was rescued by helicopter within 20 minutes and flown to hospital, but died later from her injuries.
The teenager, who has not been named, was reported by newspapers to have been part of a school group training for the annual Ten Tors Challenge, a gruelling two-day hike across the remote moors.
About 2,500 teenagers take part in the event every May. With support from the military, they walk up to 55 miles across Dartmoor, known for its extreme weather.
A helicopter took nine other members of the group from the moor, although none was injured. Police said the group of 10 boys and girls were aged about 14 and were from Devon.
In a separate incident, two people were swept to their deaths as they walked along the harbour wall at Mullion Cove, Cornwall during a storm.
Police said the man and woman were washed out to sea by a wave.
REUTERS PDM DS1505