Under the eye of local guides they were "canyoning", jumping or abseiling down the steep, rocky sides of a gorge into a white water river and then bodysurfing along the fast flowing stream.
Some 43 holidaymakers from half a dozen nations had assembled for the canyoning experience, run by local company Adventure World. They had paid Sfr90 (pounds 38) for an hour-and-a-half of an adventure which Adventure World manager Georg Hodle describes as "rafting without a raft". Customers did not even have to be able to swim, he later explained. They were, after all, kitted out with a wet-suit, life jacket, helmet and harness. Nothing could go wrong.
"Canyoning" has become a big attraction in Switzerland. The tourist town of Interlaken, 60km (37 miles) southeast of the Swiss capital, Bern, draws not only young Swiss adrenalin junkies but also adventurous young people from all over the world. At 6pm (4pm GMT), as eight guides and instructors took the group to the edge of the river, dark clouds were gathering around the nearby mountain. The guides, though, paid no notice. Weather reports had forecast clear skies, and the guides were unperturbed by the cloudburst a few miles away.
The young adventurers had to travel only 350m, abseiling down waterfalls with the aid of ropes. At its narrowest, the gorge was less than two metres wide, and the cliffs 20m high. As the afternoon progressed, the yellow helmets and bright protective clothing glinted as the enthusiasts, split into four groups, threw themselves into the rock strewn stream.
Unbeknown to them, further upstream there had been a thunderstorm which caused a flash flood of extraordinary ferocity. It rocketed down the mountainside, tore down trees and sucked along large rocks. Its impact on those in its path was terrible.
From his hospital bed, John Hall, 22, from New Zealand, told his mother what had happened next. "First of all he said a smallish wave of water came by and he said that was quite fun," Mr Hall's mother said. "But then a massive great big wall of water came along and they just couldn't cope with it."
"They just tumbled and rolled with the water down the river and down the canyon. He was upside down hitting his head against the rocks," she said. John briefly lost consciousness as he was somersaulted through the raging water. He was later taken to hospital with suspected concussion and an injured back.
Len Brajkovich said his 21-year-old daughter Kelly narrowly missed being caught in the wall of water which engulfed her friends. "She said the water was crystal clear one minute and just murk, mud and logs the next," Mr Brajkovich said from his home in Perth, Western Australia. "She went under and somebody grabbed her and she grabbed somebody else and they just clambered straight up the sides and back out of reach of the water," he said.
The first outsider to realise the scale of the disaster was Andreas Haesler, who was jogging on the shore of Lake Brienz. He saw the huge quantities of muddy water gushing from the Saxeten into the lake. "I saw huge pieces of wood in the water," said "Then I saw bodies - one on its stomach, one on its back. They were all wearing life jackets but it was clear they were dead," he said.
The seven-metre high wall of water had taken 19 people, including two guides, to their death. Two more are still missing. Four of the dead were women. At least one was from Britain. Others came from South Africa, Australia, New Zealand and Switzerland.
Investigating magistrate Martin Trapp told a press conference that identification may take weeks, because the adventurers had stripped off all personal items before donning their life jackets and helmets. Dental and DNA tests may be needed, he added. More than 150 police and rescue experts were involved in a massive search for the missing.
A team of counsellors, headed by Jean Scheiben of Bern's state police force, has been "debriefing" the survivors in Interlaken. Inevitably questions will be raised about how well Adventure World, ran their activities, despite its previous good record. "Something absolutely extraordinary, incomprehensible and unforeseeable must have happened, because our guides know every centimetre of the river," Mr Hodle said. He suggested that it was not necessary to be able to swim or even be very fit to participate in canyoning.
"If a person is able to walk for half an hour without a problem, then that person is fit for this kind of activity," he told The Independent yesterday.
Mr Hodle does not appear to be a callous man. Rather, he seems to be a victim of his industry's boast. "Much fun - no risk", is how operators advertise the pleasures of canyoning. They believed it, and on Tuesday paid the price.
Local people said they were shocked - but not surprised - about the tragedy. "I cannot understand how the people that know this region and have experience in canyoning could allow something like this to take place in these weather conditions," said Fritz Goetz, a local fisherman.
Flash floods are a well known danger to experienced canyoners. Websites from Australia to Utah discuss the danger. No caving or potholing team would set out without constant updates of the weather upstream. So what happened in the Saxeten gorge? The question also arises of why Adventure World did not keep a log of the names and nationalities of those on the trip.
Swiss government official Samuel Bhend said authorities would be examining whether there should be tighter limits on such sports. "There are questions about ... how far we should go in search of an adrenalin rush. Maybe we should learn again to respect the limits set by nature."Reuse content