Peterborough County OPP say officers rescued a driver after their vehicle crashed into Rice Lake early Tuesday morning.
Police say around 12:30 a.m., a witness reported a high-speed SUV had driven off Wood Duck Drive east of Bailieboro and ended up in the lake.
No one was seen exiting the vehicle.
Three OPP officers arrived on scene and located a nearby small boat and paddled out to the submerged vehicle, relying on the headlights shining through the water.
They entered the water and managed to remove the driver from the vehicle.
The 45-year-old Port Elgin, Ont., woman was brought to shore where paramedics first transported her to local hospital.
She was later taken to a Toronto trauma centre with life-threatening injuries.
Firefighters later worked to remove the vehicle from the lake.
The cause of the crash remains under investigation.