RCMP say 25-year-old Kevin Boutilier was houseboating with friends on Shuswap Lake in B.C. when he disappeared under the water on Saturday.
Boutilier was in a rented houseboat with several friends when someone's hat blew into the water in the Narrows area of the lake.
It appears Boutilier and several others jumped into the water to retrieve the hat, but the houseboat began drifting away because of rough water conditions.
Two of the individuals in the water appeared to be in distress, so several others dived in to assist.
RCMP say Boutilier was last seen going under the surface several times. He did not resurface in spite of a friend's efforts to aid him.
Boutilier was wearing red shorts at the time. All others made it safely back to the boat.
Rescue teams worked with police to search the area, including nearby shorelines, but found no trace of him.
RCMP say that area of the lake is very deep and the terrain on the bottom presents challenges for divers as well as using sonar equipment.
Sgt. Dave Dubnyk says it's important that people understand how quickly the weather can turn for the worse on the lake.
"I think it's deceiving to people out there," he said. "So you can go ... swimming off the boat all day long, then all of a sudden you have these big waves ... which can present very dangerous conditions for even the strongest of swimmers."
Dubnyk says he always recommends people wear a personal flotation device when on the lake. He says it's a tragic story, but unfortunately happens almost every year in the area.