(CNN)A FedEx Express driver is being hailed a hero by police after he jumped into freezing water to save a woman who had crashed her car.

Brandon Alt said he was just getting started on his delivery route that goes through Truckee, California, on Monday, when the car in front of him veered off the road and into the river below.

"As I was following her she was weaving in and out of the lane," Alt, 34, told CNN on Wednesday. "She almost hit two vehicles that were coming in the opposite direction."

They were traveling on River Road, a winding road that offers a scenic view of the area with the Truckee River on one side. The river is an outlet of Lake Tahoe and flows more than 120 miles crossing into Nevada.