Rockwall County sheriff's Lt. David Davis said Monday that nobody was hurt in the incident at Lake Ray Hubbard.
Davis says the women drove through a nearby park early Saturday and apparently got lost, in the dark, while seeking Interstate 30. The car drove down a boat ramp.
Deputy Keven Rowan was patrolling and saw the car in the water.
Rowan, in the video, is seen along the water and yells "Can you get out of the car?"
He swims to the car and uses a window-breaking device to shatter the glass and escort both women to shore.
The vehicle sinks moments later.