NELSON, British Columbia (AP) _ Helicopters crews saw no sign of the youngest son of former Prime Minister Pierre Trudeau during an aerial search Monday over the mountain lake where he is believed to have drowned.

After an unexpected break in what had been snowy, foggy weather, rescue workers began their hunt for Michel Trudeau, who was swept into an icy lake by an avalanche Friday in southeastern British Columbia.

``There's nothing visible from the surface. We're just going to have to go to the last seen point and try it from there,'' said Dave Poirier, head of a diving team that planned to attempt to recover Trudeau's body later Monday.

The divers must work quickly because Kokanee Lake was freezing over, which could put the search on hold for weeks. Helicopter crews prepared to drop explosives near the lake to clear an avalanche hazard before divers headed in.

Police have not identified the others in the group, but published reports say Trudeau, 23, and Andrew Bednarz, 23, were thrown into the lake by the avalanche. Bednarz managed to pull himself out.

The others reportedly in the group, Jeff Butcher, 22, and Bradley Hamacher, 23, huddled with Bednarz to keep him warm.

``They yelled at Mike `to swim, swim, swim' but basically just watched him go under the water,'' Paul Sinclair, who was with the group a day earlier, told the National Post.

Michel Trudeau, a passionate skier and outdoorsman like his father, knew the risks at Kokanee Glacier Provincial Park.

It is a popular spot for back-country hikers and skiers, said area manager for the province's parks service, Steve Kent. But as its popularity has grown so has the death toll, with 10 avalanche fatalities in the last decade, including six killed in one slide in January.

Police say Trudeau's group were knowledgeable about avalanche hazards and survival techniques _ even carrying locator beepers in case they were buried.

A spokesman for Pierre Trudeau issued a statement from Montreal saying Michel's parents were deeply saddened. He said they appreciated the many expressions of sympathy they have received and asked that the family be given privacy.

The former prime minister has two other sons, Sacha and Justin.