Police dragged the bottom of a lake and searched rocks around a mountain stream where a quick burst of rain turned a brook into a raging torrent.
Police spokesman Peter Abelin said sniffer dogs were also used in efforts to find the people missing after the Â"canyoningÂ" tragedy.
Â"We're not giving up hope of finding them alive. Of course the hope gets smaller as time passes,Â" Abelin said.
The largest group of victims appear to have been Australians, with 10 men and three women aged 19 to 31 feared dead.
Altogether, at least 19 people died and six were injured when a flash flood carrying rocks and debris crashed into a group of 53 canyoners in the Saxetenbach gorge, just south of Interlaken.
It happened in an instant, reports CBS News Correspondent Richard Roth. The alpine stream raged with mud and debris. Helmets and life jackets hardly mattered. Survivors phoned horror stories to relatives at home.
"He said he was just tumbling under the water, just didn't know which way was up, which way was down. He doesn't know for how long, but he reckons he went through six waterfalls on the way down," said Ann Hall, the mother of a survivor.
"Canyoning" is the name of the sport, described as whitewater rafting without a raft. Close to nature and close to danger, it draws adventurers who want vacations where there's no chance to call 911.
And that's a growing market in the travel business.
"They're looking for a little bit of an adrenaline buzz, a bit of excitement, something they can remember, something they can talk about when they get back," said Mark Anstice of Maverick Travel.
Australian and New Zealand survivors told of being hit by a wall of water, which one woman said was 20 feet high.
Â"The wall of water came through at a hell of a force and took out the first group who were on the rock level directly below,Â" Kelly Brajkovich told her father Len, The Sydney Morning Herald reported.
Â"They just disappeared. They didn't have a chance.Â"
Local residents wondered why the group went on their expedition despite visible and audible signs of the approaching storm.
The Swiss fire brigade has said it was aware of the flood on Tuesday afternoon and emergency services had sent a man to the river to try to warn the group of the danger.
The victims were part of a group of 99 young tourists camping on a tour organized by Contiki Holidays of London.
Â"We won't be offering canyoning trips anymore, anywhere,Â" Contiki spokeswoman Bernice Windley said.
A memorial service for the victims is planned for August 5 in Interlaken.
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