01
Basin Water System
The Mekong runs nearly 4,900 km from the Tibetan Plateau, where it is the Lancang, through Myanmar, Lao PDR, Thailand and Cambodia to Viet Nam's delta. The monsoon shapes it: 80–90% of rain falls between June and November, producing the flood pulse that carries sediment and sustains fisheries and farming. Lao PDR generates about 35% of annual flow. China contributes about 16% on average, but up to 24.1% or more of dry-season base flow. Cambodia's Tonle Sap Lake acts as a natural reservoir, storing up to 70 km³ in the wet season and returning about 34 km³ to the river in the dry season. The basin supported 72.1 million people in 2020.
02
Resources & Demand
Water is abundant overall, at 8,000–8,500 m³ per person a year, but not when it is most needed: the dry season carries an estimated 47.3 km³ deficit. Irrigated agriculture takes 82–94% of national withdrawals, from 82% in Lao PDR to 94% in Cambodia, and basin-wide irrigation efficiency is only 53%. The Lower Mekong Basin produces about 15% of global rice exports and around a quarter of the world's inland freshwater fish catch, and the delta grows about half of Viet Nam's rice. Demand is rising. Viet Nam projects its industrial demand to more than double, from 7.5 to 15.6 billion m³ between 2020 and 2030.
Supporting metrics:
03
Infrastructure & Governance
Hydropower is turning the Mekong into a regulated cascade. At least 45 large reservoirs hold 46.796 km³ of active storage, and China's Lancang cascade controls about 56% of it, anchored by Nuozhadu (5,850 MW) and Xiaowan (4,200 MW). Lao PDR holds 32.7% and has made hydropower an export industry, with Xayaburi (1,285 MW) on the mainstream. Governance is split. The Mekong River Commission, created by the 1995 Mekong Agreement, joins Cambodia, Lao PDR, Thailand and Viet Nam, but its consultation procedures give downstream states no veto. China and Myanmar are dialogue partners and engage through the six-country Lancang-Mekong Cooperation, which has secured year-round data sharing since 2020.
Supporting metrics:
04
Investment & Resilience
Multilateral lenders now lead investment, and the focus is shifting from dams toward cities and farms. The Asian Development Bank's USD 966 million Livable, Resilient and Water-Secure Cities programme in Cambodia is the largest, with a USD 298 million first tranche under implementation across 14 cities. The CAISAR irrigation project pairs a USD 250 million loan with a USD 18 million grant for 2025–2030, and the World Bank's USD 387 million delta resilience project is building coastal protection in Viet Nam. Sanitation lags furthest: Phnom Penh has no centralised wastewater treatment plant, and most of the basin's effluent reaches rivers untreated. In the delta, a one-metre sea-level rise could inundate up to 40% of the land.
Supporting metrics:
05
Key Challenges
- Restoring sediment flows, after reservoirs have cut downstream suspended sediment delivery by up to 50%.
- Protecting the inland fishery, where catches have fallen below 2 million tons from a historical 2.5 million.
- Coordinating upstream reservoir operations with downstream needs while the Mekong River Commission cannot enforce flow rules.
- Containing salinity in the delta, where saltwater has reached up to 130 km inland during extreme droughts.