Mekong River

The Mekong River descends from the Tibetan Plateau through a steep, deeply incised upper basin before spreading across lowlands in mainland Southeast Asia. In China it is known as the Lancang Jiang; after entering Myanmar and Laos, it forms or approaches several international boundaries before flowing through Laos and Thailand, then Cambodia and southern Vietnam.¹ Its lower course divides into distributaries that build the Mekong Delta, one of the region’s most densely settled and intensively cultivated landscapes.

Seasonal monsoon rainfall governs the river’s annual rhythm. High flows usually arrive during the summer monsoon, while dry-season levels fall substantially. Tributaries such as the Nam Ou, Mun, and Se San enlarge the lower basin, and the river’s shifting channels, sandbars, wetlands, and flood forests create a landscape in which flooding is both a hazard and a source of fertility.²

The Mekong’s flood pulse connects the main channel to wetlands, lakes, and floodplains, making seasonal inundation central to ecological productivity. In Cambodia, the Tonle Sap River reverses direction during the wet season, sending Mekong floodwater into Tonle Sap Lake; the lake later drains back toward the river. This unusual exchange expands fish habitat and helps sustain one of the world’s major inland fisheries.

The basin contains highly diverse freshwater fauna, including giant freshwater fish, migratory species, and the endangered Irrawaddy dolphin. The Mekong giant catfish is among its best-known species, but many less conspicuous fish underpin local diets and trade. Dams, altered flow timing, blocked migration routes, sand mining, pollution, and climate-driven changes in rainfall and sea level threaten these linked habitats.²³

The river is an economic and cultural foundation for communities across the basin, supplying water for rice cultivation, capture fisheries, aquaculture, transport, and hydropower. The delta is especially important for rice production and exports, while upstream valleys and plateaus support diverse ethnic communities whose livelihoods often depend on seasonal river conditions.¹

Hydropower development has transformed the basin. China operates dams on the upper Lancang Jiang, and Laos, Thailand, Cambodia, and Vietnam have developed or proposed projects on the mainstream and tributaries. These installations can provide electricity and regulate flows, but they may also retain sediment, disrupt fish migration, and alter flood timing. The Mekong River Commission was established by Cambodia, Laos, Thailand, and Vietnam through the 1995 Mekong Agreement to promote cooperation over shared water resources; China and Myanmar participate as dialogue partners.²

Several distinctive features make the Mekong more than a conventional transboundary river. The Khone Falls in southern Laos are a broad series of rapids rather than a single vertical waterfall, historically limiting navigation between the upper and lower reaches. Nearby channels and pools also provide habitat for rare river wildlife. In Cambodia, the annual expansion and contraction of Tonle Sap Lake is so closely tied to the Mekong that changes in either system can affect fisheries, agriculture, and settlement patterns.¹

The delta is also unusually exposed to coastal change. Reduced sediment delivery, groundwater extraction, river engineering, and rising seas contribute to erosion and salinity intrusion, which can move inland through canals and distributaries. Conservation therefore requires more than protecting a single channel: it involves maintaining sediment movement, fish passages, wetlands, flood storage, and cooperation among countries with different development priorities.²

Lancang Jiang

The Chinese name for the Mekong River, commonly used for its course within China.

Mekong Delta

The low-lying distributary plain in southern Vietnam where the Mekong reaches the South China Sea.

Flood pulse

The recurring seasonal rise and fall of river water that connects channels with floodplains and wetlands.

Tonle Sap

Cambodia’s large lake and connected river system, whose seasonal flow reverses in response to Mekong flooding.

Mekong River Commission

An intergovernmental body created by the 1995 Mekong Agreement to facilitate water-resource cooperation among four lower-basin countries.