Lynn Jennifer Groesbeck was driving home after visiting family when her car crashed into a concrete retaining wall and swerved off a bridge shortly before midnight on Friday.
The 25-year-old was tragically killed in the late-night accident - but her baby daughter Lily survived the impact.
"I don't know how much water was getting into the car"
However, the car - which was upside-down and partly-submerged in the freezing waters of Utah's Spanish Fork River - was not discovered until 13 hours after the crash.
A local fisherman spotted the car around noon on Saturday, and quickly alerted emergency crews.
Lt. Cory Slaymaker, of the Spanish Fork Police Department, said: "The baby was in a car seat in the backseat on the passenger side.
"The vehicle was on its top, so the car seat could have been out of the water. The car was on the embankment, so I don't know how much water was getting into the car."
He added that the water was so cold that three police officers and four firefighters who worked on the rescue were treated for hypothermia after attending the scene of the accident.
The little girl was rushed to Primary Children's Hospital in Salt Lake City, where she is now in a stable but critical condition.
According to ABC News, Lily was breathing on her own Sunday evening.
All pictures obtained via ABC News.