RCMP say the Cessna 180 was trying to take off Saturday afternoon from Pasatchaw Lake, northwest of Lloydminster, when it went down after catching a wing in the water.
The pilot and passenger managed to get out of the plane and swim to shore.
They were checked for injuries by an ambulance crew and released.
The plane was en route from Shoal Lake, Man., to Sherwood Park, Alta.
Transportation Safety Board officials are investigating.
Police say the plane had just refuelled and there was little wind, making it difficult for the pilot to get the plane off of the water.
On the third attempt the pilot managed to lift off, but the wind died down and the plane came down at an angle, catching a wing in the lake.