The Boise County Sheriff's office said it appears the driver, Thomas Anthony of Boise, was heading south on Highway 21 when his vehicle rolled and ended up going into the river.
The vehicle then washed down the stream about 100 feet until it became lodged on some rocks. A citizen spotted the vehicle in the water.
Anthony was found dead inside the car. His body was transported to the Lowman Ambulance facility.
Sunday morning, crews set up a rope system and managed to pull the vehicle out with a tow truck.
Because of the dangerous conditions, it took authorities about two hours to pull the vehicle out of the water.