No. 114: Nov-Dec 1997
The following question was posed in the September 6 issue of New Scientist.
"My wife and I saw a puzzling sight in October 1994, in the Mekong River near Nongkhai, Thailand, during a full moon, in the evening. Lights appeared under the water for a few hundred metres along the Mekong River. They rose from the bottom of the river and floated to the surface, then shot like missiles into the sky and out of sight. They were the size of beach balls, and many flew out of the water every few minutes, surfacing about 10 metres apart. I am told that this happens every year at the same time. Locals say it is caused by a serpent releasing her eggs. Does anyone know of this phenomenon?"
A. Pentecost answered. He noted first the similarity of the Mekong phenomenon to the will-o'-the-wisp or ignis fatuus. The usual explanation of ignis fatuus blames the spontaneous combustion of marsh gas. However, the Mekong lights are initially seen under the water where there would not be enough oxygen to support combustion. Pentecost suggested instead phosphorescent bacteria or the "cold flame" of phosphorus vapor which might form through diphosphane decomposition.
(Pentecost, Allan, et al; "Mekong Mystery," New Scientist, p. 96, September 6, 1997.)
References. The Mekong phenomenon may be allied with the many examples of luminous aerial bubbles. See SF#102 and a good collection of them in category GLD7 in our Catalog Lightning, Auroras.