Why go
This water cycle makes sense of landscapes you can see from Phnom Penh to Tonlé Sap: the river junction at Chaktomuk, the lake's shifting shoreline and the floodplain's role in farming and fishing. It also gives context to the Water Festival without reducing the river to a spectacle.
The full story
Most of Cambodia's major inland waters drain toward the Mekong or Tonlé Sap, while streams on the western side of the southwestern mountains run toward the Gulf of Thailand. The Mekong enters from Laos, bends across the east and reaches Phnom Penh. There, at the junction known as Chaktomuk, the Tonlé Sap River arrives from the northwest; the Mekong and Bassac continue south toward the delta. In the wet season, the Mekong rises enough to push water back up the Tonlé Sap River into the lake. The lake spreads across surrounding low land, creating a much larger flooded landscape than in the dry season. As Mekong levels fall, the Tonlé Sap River resumes its usual outward flow. Sediment and the annual flood pulse help shape the basin's fields and fisheries. This is a seasonal process, so the exact look of the shore depends on when you visit. The reversal is also the natural event associated with Bon Om Touk, Cambodia's Water Festival.