Vietnam has predicted “very high adverse effects” on the Mekong river environment and economy if 11 proposed dams are built on its lower mainstream. The warning is the result of a 2 1/2 year study submitted by Vietnam to the Mekong River Commission comprising Thailand, Vietnam, Cambodia and Laos. A commission statement released on Monday said the study, which includes 800 pages of impact-assessment reports, indicates “high to very high adverse effects on some of the key sectors and environmental resources in Cambodia and Vietnam.”

The commission said it considers the report an internal document and is not yet releasing it. Vietnam has not released it publicly. Laos is behind most new dams proposed for the lower Mekong. It wants hydropower exports to become a mainstay of its economy, which is among the least developed in Asia. The river commission, which was set up to mediate the conflicting water priorities of Mekong countries, said the Vietnamese report will help its own study, which was commissioned in 2011 and expected to be completed next year.

Much of south-east Asia is suffering a record drought due to El Niño and officials in Vietnam have said the effects are exacerbated by existing Chinese dams on the upper Mekong. The rice-bowl-sustaining river system flows into Myanmar, Laos, Thailand, Cambodia and Vietnam.