Naga fireball (Bang Fai Phaya Nak)

In local belief the lights are manifestations of phaya nak, the giant serpent (Nāga) said to live in the Mekong River. Observers and some commentators state the phenomenon is 'hundreds of years old' as a folk occurrence; however, the explicit official labeling as 'Phaya Nak lights' dates from a local council renaming in the mid-1980s, replacing an earlier local usage of 'ghost lights.' Scientific and skeptical accounts do not treat the phaya nak attribution as a physical origin but record it as the prevailing cultural explanation.

Reportedly seen as glowing reddish balls ranging from small sparkles up to the size of basketballs. Accounts describe them quickly rising from the water to heights of a couple of hundred metres before disappearing. Numbers observed vary widely across events, from tens to thousands in some reports.

Described in sources primarily as a visual phenomenon that 'emerge from the water and ascend into the air' and vanish at height. Locally attributed agency assigns the display to phaya nak, but scientific and skeptical commentators advance alternative causal accounts — including tracer rounds or flare guns fired across the river, flammable marsh gases such as phosphine, and laboratory-produced plasma analogues — and dispute spontaneous-burning-gas explanations. Sources present these competing explanations without consensus.