Police and firefighters in Anne Arundel County were called to the scene of the crash in the 200 block of Magothy Bridge Road around 8:10 p.m.
When they arrived, they found the woman sitting on the roof of her submerged car in the Magothy River. Witnesses told police the vehicle left the road, went through the woods and ended in the river then floated for a short time before it was submered, police said.
Firefighters helped the 26-year-old woman to shore. She told crews she wasn't hurt and declined a ride to the hospital.