On Wednesday evening, several people were on the wakeboarding boat on the south end of the lake when the boat operator slowed down.
The man, who was kneeling at the front of the boat, was thrown off into the water in front of the boat, RCMP Cpl. Dan Moskaluk said.
Moskaluk said the man, who was not wearing a lifejacket, was struck by the boat and did not resurface.
"At this time the individual is presumed drowned," he said.
"The search effort is resuming today with Penticton SAR out on the water along with Penticton RCMP. We do have the the RCMP helicopter air services on route to the area."