RCMP Cpl. Dave Tyreman says that early Tuesday morning, a passerby spotted the vehicle in the water near the northern Interior community of Houston.
He says police learned the vehicle left the forest service road, rolled down a steep embankment and ended up in the river.
The female passenger was rescued by first responders but the male driver is still missing.
Tyreman says alcohol is believed to be a factor in the accident.
No names have been released.