They say search and rescue members located a downed Cessna 182 just after 4 p.m. Friday (on Chappie Lake, south of Kenora.)
Police say two people were found dead and a third later died of her injuries.
Police arrived at the scene after receiving an emergency locator signal from Chappie Lake.
The victims have been identified as 41-year-old Nikolas Rajala, 40-year-old Teresa Rajala, and 36-year-old Lynn Bohanon, all of Grand Rapids, Minnesota.
Police say the three were staying at a fishing lodge in the area, and were on a fishing trip when the crash happened.
The OPP and the Transport Safety Board are investigating the cause of the crash.