Investigators said the teen was onboard a boat near Havasu Landing Casino Sunday afternoon when a monsoon struck the area, causing extremely high winds.
Authorities said there were several people in the water and the teen was trapped underneath the boat.
Lake Havasu Fire treated the girl and rushed her to Havasu Regional Medical Center.
She was eventually flown to Phoenix Children's Hospital, but died Monday due to her injuries.
The girl has not yet been identified and there's no word if anyone else was injured.