Swiss authorities charged eight people on Wednesday with causing manslaughter through negligence, following the canyoning disaster near Interlaken last year in which 21 people died.
The investigating magistrate, Martin Trapp, said three directors of the now-defunct company, Adventure World, which organised the fatal trip were among those charged.
The lead guide, two officials at the company's base and two other canyoning guides are also facing trial.
"They are accused of having led a canyoning trip into the Saxet brook in spite of the fact a thunderstorm was breaking over the Saxet valley, (and) of not having prevented this trip from taking place" said a statement issued by Berne cantonal police.
No date has been fixed for the trial, due to take place in Interlaken. The accused face fines or a maximum of one year imprisonment.
A total of 11 people were initially placed under investigation, but no charges have been laid against three of them.
The charges are the result of a year-long preliminary investigation which sought to clarify the sequence of events which led to the disaster.
A flash flood in the Saxet gorge on July 27, 1999, swept away a group of tourists taking part in a canyoning expedition. Most of those who died were Australians.
Relatives of the dead had been awaiting the outcome of the investigation before deciding whether to file lawsuits.
In a first reaction, a lawyer for one of the victims' families, Eric Blindenbacher, said the outcome of the investigation and charges were much what he expected.
swissinfo with agencies