On the full moon of the twelfth Thai lunar month, people float small banana-leaf baskets holding a candle, incense and a coin down the nearest river.

The stated purpose is to apologise to the water and let go of the past year's grievances, and the timing is practical: the rivers are at their highest after the rains. Held on the same night in the north is Yi Peng, when paper lanterns go up instead of down — one festival releasing things into the water and its neighbour into the air.