The Mekong River Explained - overview of wider CMDA area (beyond project area)

Published 30 Sep 2025

Hydrology of the Mekong and the CMDA Aquifer The Mekong River, the 13th longest river in the world, flows nearly 4,350 km from the Tibetan Plateau through China, Myanmar, Thailand, and Lao PDR, before entering Cambodia and reaching its vast delta in Viet Nam, where it empties into the South China Sea. This river sustains over 60 million people living along its course. The sediments it carries from the Himalayas enrich the Mekong Delta — often called the “rice bowl of Asia” — which feeds hundreds of millions more across the region. Beneath this fertile plain lies the Cambodia–Mekong River Delta Aquifer (CMDA). The aquifer acts as a hidden water buffer, storing and supplying groundwater that complements surface flows of the Mekong. It provides drinking water for rural households, sustains irrigation during dry seasons, and supports wetlands and ecosystems in both Cambodia and Viet Nam. However, the same pressures affecting the river — hydropower development, changing flows, and climate impacts — are also stressing the aquifer. Over-abstraction in the delta has caused land subsidence, while saline intrusion from the coast threatens freshwater resources. Together, the river and aquifer form a single, interconnected system where upstream and downstream pressures combine with groundwater dynamics to shape water security for tens of millions of people. The CMDA Project, supported by GEF, FAO, IUCN, UNESCO, and MERFI, is the first initiative to focus specifically on this transboundary aquifer. By linking science, governance, and cooperation between Cambodia and Viet Nam, the project works to safeguard both the visible flows of the Mekong and the invisible reserves of groundwater beneath it.