The wreck occurred around 9 a.m. in front of ETSU Family Physicians on Cassell Drive, according to police. Hughes was driving a 1990 Mercedes 190E when the car exited the parking lot, traveled across Cassell Drive through a construction area and over an embankment, then landed on its top in Reedy Creek.
Workers at the construction site went into the water and pulled Hughes and a passenger from the car. Kingsport Fire Department personnel identified the construction workers as Michael McDonald and Alex Mendez of Hayward Baker Construction and Lance Rice, of Thomas Construction.
Initial attempts to reach the men for comment were unsuccessful.
Hughes later died at Holston Valley Medical Center. Her passenger, Vicky Taylor, 58, Fall Branch, was treated for minor injuries.
Emergency Medical Service personnel gave the victims CPR before they were taken to the hospital.
Police said the cause of the wreck appears to be related to a medical condition.