What causes the NAGA fireballs ?

http://www.youtube.com/watch?v=JoilmoRHY_s&feature=related
Back story from what i have read :
What would you do if you were walking along a tropical river at night and it suddenly began burping up egg-sized balls of red light? It happens every year in October along the Mekong river (the same one featured in classic Vietnam movies like Rambo II and the flashbacks from Rambo III). The phenomenon is known as the Naga Fireballs, and experts agree that it is “just weird as shit.”
What happens is this: starting under water, tens to thousands of glowing red lights are seen rising out from the bottom of the river, then lifting hundreds of feet into the sky before disappearing.
It literally appears that the river is spitting out flaming M&Ms. They have never harmed anyone, and don’t even seem to touch anything let alone set anything on fire. However, both of those facts were probably unavailable to dull the ferocity of the pant-crapping that took place when the event was first witnessed.
The Naga Fireballs are viewed by thousands of people every year, and a healthy number of videos documenting the phenomenon are hosted on YouTube,