A river with two directions
The Tonlé Sap river connects the lake of the same name to the Mekong at Phnom Penh. For most of the year it drains the lake southward. When the monsoon raises the Mekong faster than the lake can empty, the flow stops, hesitates and then runs the other way, pushing water inland for months.
The lake swells from roughly 2,500 square kilometres to something over 10,000, and shallow forest along its edge spends half the year underwater.
Why Angkor was built where it was
That flood pulse is the engine of the fishery, and the fishery is a large part of why a city the size of Angkor could exist here at all. A predictable annual flood that stocks a lake with fish is, in practical terms, a food supply that does not depend on a good harvest.
Reading the Bayon's reliefs with that in mind changes them: the fish and the boats carved along the lower registers are not background detail, they are the economy.
The day it turns around
Bon Om Touk, the Water and Moon Festival, falls when the flow reverses back to normal at the end of the rains. It is the largest gathering in the Cambodian year, and it is timed by the river rather than by a calendar anyone controls.
Which is the part worth carrying away. The festival is not a commemoration of something that once happened; it marks something that is still happening, on a schedule the river sets.
