Bonn Om Tuk is one of Cambodia’s most important festivals.
Heavy rains in the preceding months cause the hugely increased volume of the Mekong River to force the Sap River (which runs from the southeastern corner of Tonlé Sap lake to join the Mekong and Bassac rivers at Phnom Penh) to back up, and finally reverse its course, flowing northwards to flood the Tonlé Sap with vast quantities of fresh water and rich sediment. Then, in mid-October, as the cool, dry winds begin to blow from the north and the level of the Mekong diminishes, the flow of the Sap is again reversed, carrying the surplus waters of the Tonlé Sap southwards to the Mekong and Bassac deltas. The annual flooding of the Tonlé Sap makes the lake an incredibly rich source of fish, while the farmland around it benefits from an annual deluge of rich sediment.