The girl, who is from the Leicester area, fell from the Splash Canyon water ride at Tamworth-based Drayton Manor Theme Park on Tuesday afternoon.
A West Midlands Ambulance Service spokesman said: "On arrival, crews discovered a girl with serious injuries who had been rescued from the water by park staff.
"Ambulance staff administered advanced life support before she was flown to Birmingham Children's Hospital with the doctor continuing treatment en-route.
"Unfortunately, shortly after arrival at hospital the girl passed away."
Police superintendent Carl Ratcliffe said: "Specially-trained officers are supporting the girl's family at this difficult time. Our thoughts are very much with her family and friends following this tragic incident."
The Health and Safety Executive is investigating.
The ride was closed following the incident.
The theme park's website states the ride, which opened in 1993, features up to 21 boats, each with up to six people in.
It is open to anyone at least 0.9m (3ft) tall, although those under 1.1m must be accompanied by an adult.
The website promises "a wild ride" with "fast-flowing rapids".
It adds: "Swerve around corners, splash through the waves, and get soaked as your boat is swept along our fast-flowing rapids. No two experiences are ever the same ...
"You'll feel like you're in the middle of the jungle as you speed, bounce, and splash your way around our river, past other rides and through the trees, experiencing the most unpredictable and thrilling of river rapid rides. It's called Splash Canyon for a reason."
The theme park said: "The Splash Canyon ride has been closed following an incident this afternoon. Emergency services are at the scene and our fully trained park staff are assisting."
A spokesman for the Health and Safety Executive (HSE) said: "The HSE has been made aware of today's incident at Drayton Manor and is making initial inquiries along with emergency services."