An 11-year-old schoolgirl has died after falling from the Splash Canyon ride at the Tamworth-based Drayton Manor Theme Park.
Police said the girl, believed to be from the Leicester area, was airlifted to Birmingham Children's Hospital but later passed away.
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."
Other incidents at UK theme parks
The Drayton Manor closure is the latest incident involving a ride at a UK theme park.
Here are the details of others in recent years:
More than 30 thrill-seekers were left stuck on a rollercoaster at Alton Towers in September last year - 15 months after the notorious Smiler crash which left riders with life-changing injuries.
In May last year, the Velociraptor rollercoaster at Paultons Park near Romsey in Hampshire broke down just a week after opening.
Around 20 people had to be evacuated after what a spokesman said was a "minor fault". The ride re-opened later that day.
Two months earlier, eight people had to be rescued from the Tornado rollercoaster at M&D's theme park in Motherwell, near Glasgow when it stopped working 20 feet above the ground.
No-one was injured and the ride was closed while the theme park investigated.
In June 2015, five people were seriously injured in a collision on the £18 million Smiler rollercoaster at Alton Towers. An investigation found a computer block stopping the ride because of a stationary car on the track was over-ridden by staff, causing the crash.
As a result, the full carriage ploughed into the rear of the empty car. Leah Washington, then aged 17, had to have her left leg amputated above the knee - while Vicky Balch, then 19, also lost a leg in the crash.
The Smiler ride was temporarily closed in November 2013 after plastic guard wheels came loose and hit front-row riders.
The 14-loop rollercoaster, which took more than eight months to build, was shut for four days in July that year after a piece of track became dislodged, and was closed again for five days the following month because of another technical issue.
In July 2011, a number of people on a ride at M&D's theme park were stranded for more than eight hours when it came to a halt 60 feet above the ground.
In June 2006, firefighters had to rescue eight children and four adults trapped 40ft above the ground on the Terror Rack ride at the Pleasure Island park in Cleethorpes, Lincolnshire. It took the fire crews about an hour and a half to bring the people down to the ground after a safety device kicked in and halted the attraction.
In July 2005, four people were injured when a car came off its track at Ocean Beach amusement park in Rhyl, north Wales, when they were hit by another car.
A 32-year-old woman and 30-year-old man were taken to Glan Clwyd Hospital for treatment to chest injuries. Two other people received minor injuries and did not need treatment.
The previous year, a 16-year-old girl plummeted to her death from a ride at Oakwood theme park near Tenby in west Wales.
Hayley Liane Williams, of Pontypool, south Wales, died after falling from the Hydro Ride.
She plunged 100 feet from the ride on April 15, 2004. Swansea schoolboy Martin Rothwell, aged 10 at the time, was hit in the head and injured by the teenager as she fell past him. Safety changes were later made to the ride.
In November 2006, a French firm was found guilty of breaches of health and safety law after the death of a 20-year-old student on a rollercoaster.
Durham University student Gemma Savage died when two cars collided on the Treetop Twister ride at the Lightwater Valley theme park, near Ripon, North Yorkshire, on June 20, 2001.
Paris-based Reverchon Industries SA, which manufactured and supplied the ride, was found guilty at Leeds Crown Court of two charges of failing to ensure its safe design and construction, and failing to give information necessary to ensure the ride was safe when open to the public.
In July 2002, teenager Salma Saleem plunged 30ft from a Ferris wheel at Gulliver's World in Warrington, Cheshire.
It was not clear how the 15-year-old, who had Down's Syndrome, managed to fall from the gondola, but Chester Crown Court - which fined the operators £80,000 - heard that locks on the restraining lap bars had a history of breaking.