Naga Fireballs

Every year around Ok Phansa, the end of the Buddhist rains retreat in October, crowds gather on the banks of the Mekong at Phon Phisai and other points in Nong Khai and Bueng Kan to watch glowing red, pink and orange balls rise silently from the water and climb a couple of hundred metres before vanishing. Counts range from a few dozen to thousands. Locals attribute them to the Naga king, the serpent who lives under the Mekong and honours the Buddha with fire.

Villagers once called them ‘ghost lights’; in the mid-1980s the local council named them Phaya Nak lights, and a festival now draws tens or hundreds of thousands of visitors. In 2002 a documentary on Thai TV claimed Lao soldiers were firing tracer rounds from the far bank, and a government team under science official Saksit Tridech investigated. A Chulalongkorn University scientist, Jessada Denduangboripant, concluded from footage that flare guns fired from the Lao side produce the effect; Lao authorities denied any firing, including in a 2021 inquiry.

Other explanations include methane and phosphine produced by decaying matter in river mud that ignites at the surface, similar to will-o’-the-wisp, though skeptics such as Brian Dunning argue this is not supported by observations and note the lights rise silently and in calendar-linked bursts. Plasma balls have been proposed, but only appear in laboratory experiments.

For many Thai and Lao Buddhists the event is a moment of faith and a tourist spectacle at once, so the debate is a matter of respect as much as science.

Silent, egg- to basketball-sized reddish balls that shoot up from the water, from a few to thousands in a night.

A stretch of the Mekong around Phon Phisai, Nong Khai and Bueng Kan, mostly at night around the full moon of the eleventh lunar month, in October.

The Phaya Nak festival at Nong Khai includes boat racing, ceremonies and nightly vigils, and is an important part of Isan identity.