Temperatures may have dropped in much of the country, but authorities and seasoned snowmobilers are cautioning that many trails aren't properly frozen.

The warning comes days after fatal snowmobile crashes in Whistler, B.C., and Kings County, N.S.

The B.C. crash happened at about 11 p.m. on Friday, on Blackcomb Mountain.

Tour company Canadian Wilderness Adventures says an Australian man, 65, lost control of his vehicle and struck a tree near the end of his dinner-and-snowmobiling-tour.

"For some reason the client lost control of the snowmobile and it just veered off the trail and powered into the woods," company co-owner Allan Crawford told CTV Vancouver.

The man was pronounced dead on scene and a female passenger, 54, was taken to hospital.

The company says the man did not have any alcohol with his dinner that evening.

The RCMP and Coroners Service are both investigating the cause of the crash.

On Saturday, a second fatal crash occurred on the other side of the country.

In this incident, a 29-year-old woman died after crashing into a tree off a groomed trail.

A 35-year-old Ottawa man was also seriously injured in a crash on Friday. He was airlifted to a trauma centre with "multi-system trauma" after he hit an object under the snow and was thrown approximately 30 feet from his vehicle.

And on Sunday, a man in the Township of King, Ont., suffered life-threatening injuries when police believe he rode a snowmobile into a boat on a rural property.

The man remains in hospital and York Regional Police are currently investigating the crash.

Now, snowmobile clubs and police are warning riders to take extra care before they set out on the vehicles.

In Ottawa, the head of the local Rideau Snowmobile Club said winter's late arrival in the city means it's still not safe to ride over waterways.

"There's a lot of water underneath the snow in places," Wayne Averie said. "They're not frozen at all yet."

Club members say, if cold temperatures keep up, they hope the trails will be ready for drivers in two weeks.

The Ontario Provincial Police also released a list of tips to keep snowmobilers safe.

Officers are advising drivers to:

Service their sleds and inspect their gear before heading out onto the snow

Stay connected with friends, family or emergency contacts and use the buddy system

Carry a repair, first aid and survival kit

With files from CTV Vancouver, CTV Atlantic, and CTV Ottawa