Naga fireballs

The Naga fireballs are a phenomenon seen in the Mekong river—in Thailand and in Laos—in which glowing balls rise high into the air. The balls are reddish and about the size of chicken eggs; they rise a couple of hundred meters before disappearing. The number of fireballs is variable, being reported at between tens and thousands per night. The fireballs are most often reported around the night of Wan Awk Pansa at the end of the Buddhist rains in October. It has been proposed that the balls are produced by the fermentation of sediment in the river, which can supposedly combust in the particular river and atmospheric conditions of the nights in question.

From: http://en.wikipedia.org/wiki/Naga_fireballs