At least three Swiss soldiers have died and two are still missing following a military exercise on the River Kander near Wimmis in canton Bern.
The latest tragedy to hit the Swiss army comes less than a year after six mountain specialists were killed as they climbed the Jungfrau in the Bernese Oberland as part of their training.
The defence ministry confirmed on Thursday that another five men were in hospital - two in a serious condition - but was unable to give the precise cause of the accident, which happened late in the morning.
"It is a sad day for the army," said military spokesman Felix Endrich at a news conference in Spiez. He was able to add though that the two seriously injured men were out of danger.
Defence Minister Samuel Schmid called off a planned trip to Brussels for a Nato meeting after hearing about the accident. Speaking in the Swiss capital Bern, he said he was dismayed and sad and that his thoughts went out to the soldiers' families.
The alarm was raised around 11.30 am. Two rubber dinghies overturned on the river, which was flowing at a rate – 40 cubic metres per second – that is considered unexceptional.
There were no storms in the area either that could have increased the flow according to the Swiss national weather service, Meteoswiss.
However, locals told swissinfo that water levels were high and that the stretch of river where the accident is believed to have taken place is graded as highly difficult for rafting. Commercial rafting is effectively banned there according to Swiss radio reports.
Cantonal police spokesman Otto von Almen told swissinfo that around 80 people participated in the rescue effort to find the missing soldiers.
These included 40 army personnel, 20 police, two helicopters with infrared cameras, 12 members of the local fire department, four lake police staff with divers as well as six members of the Swiss Alpine club with rescue dogs.
The search, which was suspended overnight, covered a ten-kilometre stretch leading to Lake Thun.
Air force commander Walter Knutti, speaking to journalists late on Thursday evening said that the three bodies that had been recovered were all wearing lifejackets and helmets. He also admitted that it was unlikely that the two men still missing had survived.
Endrich told swissinfo earlier in the day the soldiers were on a refresher course.
"It's quite usual if they have an order, for example, to set up a temporary airfield somewhere in Switzerland to secure the zone," he explained. "The troops come to the area, secure and prepare the airfield so helicopters can land."
However according to Knutti, exercises involving boats were not part of the usual training for these soldiers. It is now believed the boating incident happened during a team-building exercise.
These security specialists were based in Wimmis for their course, but they are normally attached to the Alpnach airfield in canton Obwalden.
A military investigation is already underway to determine the exact cause of the accident and if anyone in particular is responsible.
The latest fatal incident involving the Swiss army follows the death in July 2007 of six mountain climbers who were hit by an avalanche on the southwest flank of the Jungfrau peak – Switzerland's worst military accident for 15 years.
Questions were raised at the time about whether the army had underestimated the risks and the armed forces were severely criticised by the media.
Last October, the military justice launched a criminal investigation against two mountain guides. Scientific analysis had shown that the soldiers were most probably carried away by an avalanche they triggered themselves as they climbed towards the famous summit.
The army's investigating judge said at the time that the guides' decision to proceed with the climb was debatable given the conditions.
swissinfo, Dale Bechtel and Scott Capper
Recent army accidents
July 12, 2007: six recruits die in an avalanche on the Jungfrau in the Bernese Oberland, the worst accident in 15 years for the armed forces.
October 12, 2001: an Alouette III helicopter hits a cable near Crans-Montana in canton Valais and crashes, killing all four people on board.
May 25, 2001: an Alouette III helicopter hits a cable near Delémont in canton Jura, killing the pilot and three border guards.
November 12, 1997: a Pilatus Turbo-Porter aircraft crashes during an exercise near Simmental in canton Bern. The pilot and four passengers die.
June 22, 1994: a civilian helicopter collides with a Swiss army Super Puma helicopter and crashes. A British couple and the pilot are killed.
April 27,1993: an army Pilatus Porter is caught up in high winds and flies into a cliff on the Finsteraarhorn in canton Bern. Three people die.
November 2, 1992: six people die when a munitions depot blows up near Susten in canton Bern.