Wanderlust World Wanderlust World Phnom Penh has been Cambodia's capital since 1434 (with interruptions). It sits at the confluence of three rivers: the Tonlé Sap, the Bassac, and the Mekong—but the city center and historic core line the Tonlé Sap River, not the Mekong mainstem.
The Tonlé Sap River is the outlet of Tonlé Sap Lake, Southeast Asia's largest freshwater lake. During the dry season, the river flows out of the lake into the Mekong. During the monsoon, the Mekong's flood pulse reverses the Tonlé Sap's flow, filling the lake to 5–6 times its dry-season size. This "heartbeat" drives one of the world's most productive inland fisheries.
The Mekong is the basin's master artery, and Phnom Penh sits at its junction with the Tonlé Sap and Bassac. Maps often label the entire waterfront "Mekong." But the Royal Palace, the riverside promenade (Sisowath Quay), and the historic port face the Tonlé Sap.
Phnom Penh's identity is inseparable from this three-river confluence—and the Tonlé Sap's extraordinary seasonal reversal.