A river in Thailand randomly shoots red fireballs into the air. No one knows why.

Nongkai is one of northeastern provinces in Thailand that border Laos, the border stretching for 320 kilometers (512 miles) along the Mekong River; the river that is the seat of the unsolved mystery. Here’s how the legend goes.

There exists a serpent-like creature going by the name King of the Naga embedded in the folklore and Buddhist culture. The serpent is rumored to reside deep underneath the Mekong River in an underwater city called the Muang Badan. The Paya Naga and its supernatural powers is believed to influence every aspect of their daily lives, the people here; from house building to their schools management, hotels, factories and so on.

Closely related to their Laos counterparts are the people of Isan, on the opposite banks of the Mekong; they share the same beliefs in the Paya Naga and the baffling Bang fai – the local name given to the fireball in question (the Naga Fireball). On the last day of the Buddhist lent in October each year, the Naga Fireball can be spotted as it shoots red fireballs from beneath the waters of the Mekong into the air.