Firefighters were scrambled to the blaze at the Europa Park in Rust, Germany.
The theme park is the biggest of its kind in Germany, and second most popular in Europe after Disneyland Paris.
Flames ripped through The Pirates of Batavia attraction and parts of the park were evacuated.
It is described as a “water-dark ride” and is said to be around 400 metres long. Several rides and a warehouse have also been damaged in the fire, according to cops.