The Mekong Lights mystery is one of those fantastic manifestations of nature that science has yet to adequately explained. Apparently, in the Mekong River, near Nong Khai, Thailand, lights will appear under the river within a length of a few hundred meters. These lights slowly float to the surface and then shoot out like missles into the sky and out of sight. They are the size of beach balls. The local name for them is the Nekha lights. The Nekha is a large fish which lives in the river. Locals also claim the lights are actually the eggs layed by a giant serpent. Many people travel to see them and they appear during certain parts of the year. The lights have been filmed and broadcast on Thai television, and appear to be a valid phenomenon.

One explanation is that this may be a similar phenomenon to will-o-wisps, or marsh gas. Hydride diphosphane, a reduced form of phosphorous, has a low vapor pressure and will spontaneously combust on contact with oxygen. It is unclear how hydride diphophane could contact oxygen underwater, but the rising lights may just be phosphorous luminescence. Another possibility is that this is the activity of bioluminscent bacteria. Bacteria also build up reduced phosphorous compounds in decaying phosphorous rich organic matter. This is the source of a phenomenon known as 'corpse-candles' seen in church cemeteries.

Another possible explanation is that the lights are an optical illusion of the moon's reflection. Reports of these lights correlate with the appearance of a full moon and regular waves across the water surface may create the illusion of many lights moving simultaneously.