The Mekong River Commission (MRC) said low dry-season river flows have caused a decrease in water levels in the Tonle Sap Lake, and called on all Mekong countries to improve river management.

In a press release on June 30, it said lower flows in the river during the 2019 and 2020 wet seasons decreased return flows and seasonally flooded areas in the Tonle Sap Lake area on which many Cambodians rely for their livelihoods.

This triggered adverse impacts, according to the MRC report, on agriculture, the ecological balance, reduced nutrient-rich sediment, and transportation as well as decreased fish catch in the lake area.

MRC Secretariat has urged for improved exchange of information to improve water resource management in the lower Mekong basin.

The MRC’s 18-page report encourages MRC member countries

and dialogue partners to share data to gain a deeper understanding of recent changes in the river and to address any potential impact on river communities.

“For the sake of better management of the basin and good cooperation, both member countries and China should notify any planned major changes in the operation of hydropower projects and share that information with the MRC secretariat,” MRC secretariat chief executive officer An Pich Hatda said.

“This is important as such operations may result in abnormal rises and falls in water levels,” he said.

Cambodia National Mekong Committee secretary-general So Sophort could not be reached for comment on June 30.

Member countries are obligated to “help the acceptable natural reverse flow of the Tonle Sap River to take place during the wet season” and prevent human-made peak flows that would not naturally occur during the flood season, according to MRC.

The press release said rainfall in April–May was the highest on record in some places for these months for the last 18 years. This was particularly obvious in the middle part of the lower Mekong basin areas of Thailand and northern Cambodia.

“But overall, river flows did not increase significantly. Rapid changes in water levels due to hydropower operations in the upper Mekong continued in 2021,” it said.

The report said such changes may have impacted navigation, river ecosystems, and riverbank stability, although more study is needed to pinpoint the type and extent of impact.

“The report notes that releases from storage dams increased dry season flows above the long-term averages for most of the dry season, with both positive and negative consequences,” the press release said.

“Increases in dry season flows could be beneficial for agricultural production and navigation and combatting seawater intrusion in the Mekong Delta,” it said.