Alert: 02/22/2025
A sudden release of water at dams in China will cause the Mekong River to rise 0.50 meters at Chiang Saen, Thailand on February 24.
Spotlight
Mekong Floodpulse Contracts in Early October for the First Time in Four Years
As we predicted in our last update, over the past two weeks the Mekong Floodpulse contraced from 18,500 square kilometers to 17,100 square kilometers of seasonal inundation. This is significant as we have observed for the last four years the floodpulse reduction beginning at the end of October or at the beginning of November. While reverse flow from the Mekong mainstream into the Tonle Sap was normal for the wet season–and much higher than recent years–low lake levels at the start of the wet season and a lack of rainfall over the lake throughout the season appear to be the main drivers of the early floodpulse peak. It is uncertain what the effect of the early peak will be. We do not think this is necessarily an indicator of a poor fish harvest for 2026 into 2027.
What Happened Last Week?
- Where’s the Water: Last week saw a small net restriction of water (430 million cubic meters) across the Mekong. Major dam restrictions were observed at Huangdeng (PRC, 201 million cubic meters), Xiaowan (PRC, 210 million cubic meters) and Nam Ngum 1 (LAO, 219 million cubic meters). Where is the water?
- River Levels: Levels along the Mekong are much lower than normal for this time of the year. Chiang Saen, Thailand is already at low levels common to the dry season. See how this looks.
- Where’s the Water: Last week saw a small net restriction of water (430 million cubic meters) across the Mekong. Major dam restrictions were observed at Huangdeng (PRC, 201 million cubic meters), Xiaowan (PRC, 210 million cubic meters) and Nam Ngum 1 (LAO, 219 million cubic meters). Where is the water?
Image of the Week
Late September Floodpulse could be a 2026 peak.
The image shows a total 18,500 square kilometers of Mekong Floodpulse in late September—an impressive increase from early September’s 11,900 square kilometers of flooding. Despite the improvement, MRC monitoring of reverse flow into the Tonle Sap shows 2026’s reverse flow ended on September 27. This suggests that the Tonle Sap Expansion, the main indicator of the Mekong Floodpulse, peaked two-to-three weeks earlier than it has in recent years. Despite this year’s reversal measuring as the highest volume of reverse flow since 2018 according to the MRC, two factors prevented a meaningful expansion of the Tonle Sap Lake: Low lake levels at the start of the wet season and a lack of rain in Cambodia. Reasons for the low lake levels require further study, but high reverse flow with a weak expansion is unusual for the Mekong. Typically, the Mekong Floodpulse peaks just after Tonle Sap reverse flow ends, suggesting that without a lot more rain, the image may represent 2026’s peak floodpulse. In contrast, over the past four years, the Mekong Floodpulse peaked in late October. An early peak suggests an early start to the dry season.
Where is the Water?
How Wet is the Mekong Basin?
- Click or hover over icons on map for more details.
How Much Water is in Reservoirs by Country?
Current volume (billion cubic meters) of usable water across the 45 largest reservoirs in the Mekong Basin.
How Much Water is in the Largest Reservoirs?
- Hover over chart to track reservoir volume for any particular week during the year.
How Strong is the Floodpulse?
Where did River Flow Come From?
How Wet is the Mekong Floodplain?
What Should River Levels Be?
Chiang Saen Gauge (Thailand) [UNDER MAINTENANCE]
Stung Treng Gauge (Cambodia)
Chau Doc Gauge (Vietnam)
For more info, click Natural River Flow Models in the top menu.
How do Dams Impact Different Points along the Mainstream?
How was the Weather Last Week?
- Click on maps to expand and for more details.
For more information, click Compare Maps and Data in the top menu.
Which Dams Impacted the Most?
- Click or hover over icons on map for more details.
Reservoirs with an estimated change of more than 50 million cubic meters (m³) of water over last 7 days.
For more info, click Virtual Gauges in the top menu.
Current Reservoir Volume for 58 Dams
- Hover over reservoir bars to see current or potential volume
For more info, click Virtual Gauges in the top menu.