Officer Mark Todd was the first on the scene of the crash along the 700 block of W. Cypress Street in Kennett Township just before 10 a.m., local police said.
Todd reported seeing the car nearly completely submerged in Red Clay Creek, with only the back of the car floating but rapidly sinking, according to Kennett Square police.
He was able to pull the driver from the car and bring her to shore, where she was treated by fire and EMS personnel, police said.
The driver is apparently in her 50s and was taken to a local hospital for treatment, 6abc reports.
"This is a true example of heroism at work here in Kennett Square Borough to save another human life," Chief William T. Holdsworth said.
"We could not be more proud of the selfless acts demonstrated by Officer Todd without consideration of his own safety or wellbeing."
Click here to follow Daily Voice West Chester and receive free news updates.