A new report examines how dam driven river changes are harming a Mekong flooded forest and how smarter water management could help reverse losses.
31 October, 2022 – Stung Treng Ramsar Site, Stung Treng Province (Cambodia). An aerial view of the flooded forests on the Mekong River between Stung Treng town and the Laos border. In 1999, 14,600 hectares of the site was designated as a wetland of international importance under UNESCO’s Ramsar Convention. Credit: Andy Ball
Along a quiet stretch of the Mekong River in northeastern Cambodia, a vast flooded forest is disappearing in plain sight. This report tells the story of how upstream dam operations far beyond Cambodia's borders have quietly transformed seasonal river flows, undermining a forest that depends on predictable dry season lows to survive. Drawing on satellite imagery, river data, and local testimony, it shows that what once sustained biodiversity, fisheries, and livelihoods is now being steadily eroded. The findings reveal not only what is being lost, but how small changes in dam operations could still help restore one of the Mekong's most important ecosystems.
Common tree species in the STRS serving as host for a Ficus tree. Credit: Andy Ball
Executive Summary
A large flooded forest, which covers much of the Stung Treng Ramsar Site (STRS), is a unique riparian ecosystem that underpins regional biodiversity and local livelihoods in northeastern Cambodia. Since 2008, upstream hydropower development in China and Laos has substantially reshaped the dry‑season hydrology, raising minimum river levels by more than one meter during much of the dry season, and essentially erasing a period of low‑flow that the forest requires to survive.
This report shows:
(1) dry‑season discharge at Pakse (the nearest Mekong mainstream gauge upstream of STRS) now remains above the pre‑2008 mean throughout January-May (core months of the dry season), with a series of weeks exceeding 150% of the historical mean and other weeks exceeding 200%;
(2) cumulative dry‑season releases from major dams in China and Laos are the cause of high levels during the dry season;
(3) remote sensing analysis shows an 18% (500 hectare) decline in the flooded forest extent across whole of STRS between 2018 and 2026, with some hotspots experiencing 35-59% loss.
These findings lead to the conclusion that for the flooded forest to survive, major upstream dams must reduce and/or reschedule dry‑season releases (especially February through May) and shift some releases to November-December. In parallel, STRS management should focus on safeguarding deep pools and erosion hotspots and establishing active monitoring methods to enable adaptative interventions.
Read the report on the Stimson website.
