Countries in the lower Mekong River region should delay any decisions about building hydropower dams for 10 years, an influential new study said Friday, warning of the many risks involved.

The recommendation was made in a Strategic Environmental Assessment (SEA) report commissioned by the Mekong River Commission (MRC), an inter-governmental advisory body that deals with all Mekong River-related activities.

The MRC -- which represents Cambodia, Laos, Thailand and Vietnam -- is studying the possible construction of 11 hydropower projects on southeast Asia's longest river.

"The recommendation to defer dam construction for a 10-year period is very significant," said Tiffany Hacker, an interim communication advisor for the MRC.

Environmental groups have long objected to damming the river, arguing that it would damage fragile ecosystems.

The assessment, led by consultants with the help of the MRC, government agencies and civil society representatives, said more time was needed to study the risks that come with building dams in such a complex environment.

"The mainstream projects are likely to result in serious and irreversible environmental damage and... losses in biological diversity and ecological integrity," the report said.

It also warned that the dams would have a negative impact on fisheries and could "lead to increasing food insecurity for millions of people".

The MRC stressed that it was under no obligation to follow the report's recommendations, but Hacker told AFP that member countries were "likely to take the findings seriously".

The four countries will now study the findings "for at least six months" before deciding on how to proceed, Hacker said.

More than 60 million people rely in some way on the river, which is the world's largest inland fishery, according to the MRC.

The wildlife group WWF has warned that the Mekong giant catfish -- one of the world's biggest freshwater fish -- could be driven to extinction if plans to build hydropower dams on the river go ahead, blocking spawning grounds.