Two children who were in the car when it entered the water last night were able to get out and were rescued from the water by people on the quay.
They were taken to CUH where they were treated for non-life-threatening injuries.
Naval divers arrived at the quay and located the body of the woman in her 40s following a search.
The woman's body was removed from the scene and a post-mortem is due to take place.
In a statement to RedFM News, Garda Press say the results of the post-mortem examination will determine the course of the investigation.
Emergency services including the Gardaí, National Ambulance Service and the nearby Fire Service from Anglesea Street were alerted to the incident by passersby close to 8:45pm last night.
Rescue Helicopter 117 from Waterford was also tasked to the scene.
