Supernatural phenomena always seem to be met by photographers who possess a supernatural ability to botch a simple photograph, and the Naga Fireballs phenomenon of the Mekong river in Thailand is no exception. Images of these glowing, egg-sized orbs are always grainy, indistinct, and from a distance, but one factor does lend these fireballs the credibility that its supernatural cousins lack—thousands upon thousands of eyewitnesses every year for over a century. In fact, the fireballs have been observed by so many people that their existence is not really debated, rather it is their cause that prompts lively discussion.

Locals claim that these fireballs are the product of the “Naga,” a large magical serpent who patrols the river. Every year, around the end of October, hundreds of locals and tourists gather to watch the pinkish-red, glowing orbs emerge randomly from the water, and soar into the sky without a sound or smoke trail. The number of fireballs varies from year to year, but according to locals, the fireballs have occurred annually as far back as generational memory can reach.

The attempts at scientific explanations leave much to be desired, such as the idea proposed by Manas Kanoksin, a doctor from Nong Khai. He strongly believes that fermenting sediment on the river’s bottom causes pockets of methane gas to form, and that the Earth’s position in relation to the sun during those days of the year causes them to rise, then spontaneously ignite in the presence of ionized oxygen. But other researchers dismiss this claim, pointing out that the rocky river bottom doesn’t have much sediment, and that the water’s turbulence would break up any such methane bubbles before they reached the water’s surface. A similar hypothesis suggests that the fireballs are a result of flammable phosphine gas generated by the marshy environment, but this does not address the mechanism of ignition. Still others lay their suspicions on seldom-seen but oft-blamed meteorological phenomena such as ball lightning or St. Elmo’s Fire.

The most likely explanation, of course, is that the fireballs are man made, using fireworks, flares, burning balloons, tracer bullets, or other ascending light sources—and the real mystery is how the hoaxsters have avoided detection for over a century.