Ross Nelson, 20, was trying to swim across with a friend when they both began to struggle.
A fisherman on the bank waded in to help the pair and managed to pull one of the men to safety using his rod.
Another fisherman launched a rubber dinghy to try to rescue Mr Nelson, but the swimmer slipped beneath the water before he could be reached.
The accident, which sparked a rescue operation involving helicopters, the emergency services and the International Rescue Corps, happened at Loch Lubnaig in Perthshire on Sunday evening.
Central Scotland police said Mr Nelson, from Maddiston, near Falkirk, was one of a group of five people, four men and a woman, who had driven to the beauty spot.
They parked on the east shore, at the southern end of the loch, and walked round to the west bank.
A spokeswoman for the Stirling-based force said that three of the group later decided to walk back to the east shore, but Mr Nelson and one of the other men decided to swim back across 125 metres of cold, open water.
She said: "They got into difficulties about halfway."
As they struggled, a fisherman waded into the water and held out his rod for the swimmers to grab hold of, while another on the east shore launched a rubber dinghy and began to paddle out to the pair.
One of the men managed to get hold of the end of the fisherman's rod, and was pulled to safety, but Mr Nelson disappeared under water as the dinghy approached.
A spokeswoman for the International Rescue Corps said the team found his body using underwater cameras.
A Royal Navy spokesman said a Sea King helicopter was dispatched to the incident from HMS Gannet at Prestwick, Ayrshire, and rescuers used night vision goggles to try to locate Mr Nelson, without success.
He said: "The helicopter crew were told where the person had been last seen in the water. They flew at 200ft above the loch so as not to disturb the water and even tried using night vision goggles to find him.
"But the aircraft landed after a time and the crew spoke to inspectors on the ground. They couldn't find him as the water was too murky."
Members of the Grangemouth-based International Rescue Corps located Mr Nelson under the surface, and his body was recovered by a police frogman and pronounced dead at the scene.
Park rangers at the scene estimated the water temperature to be no higher than 4C.
One said: "It looks inviting, but it's very deceptive. We try to tell campers that they have to take the water seriously. Open water saps your energy. It's not a giant swimming pool."