Great Balls of Fire

Mysterious fireballs regularly seen rising out of the Mekong River are said by locals to come from a mythical serpent called Naga that lives in the water; and by scientists to be simply flammable phosphine gas rising from the riverbed and igniting. Their number and intensity increase around the full moon of the 11th lunar month in October, marking the end of the rainy season and giving rise to an annual two-day festival traditionally held in Nong Khai province in the northeast of the country across the border from Laos. The riverside festival features Longtail boat races, a sound and light show, and – with luck – fireballs.

Source: tourismthailand.org