The survival of some of the world's largest freshwater fish - including a giant catfish - is threatened by a series of hydro-power dams planned for the Mekong River, a leading environmental group has warned.

The construction of a particular dam in northern Laos would disrupt the migration of four of the world's top 10 largest freshwater species to crucial spawning grounds, the World Wide Fund for Nature (WWF) has said.

In its report 'River Giants: Giant Fish of the Mekong', WWF said the catfish that grow up to 350 kg and freshwater stingray that can weigh in at 600 kg, would be threatened with extinction if the plans go-ahead, says a Telegraph report.

China has already completed four hydro-power dams on the Mekong, while another 11 are being built or planned in Laos, Thailand and Cambodia. Other smaller dams are proposed along its tributaries.

The Mekong is south-east Asia's longest river, rising in Tibet and flowing through southern China, Burma, Laos, Thailand, Cambodia and Vietnam before reaching the South China Sea.

But WWF's most pressing concern in the hydropower plant planned for Sayabouly province, in Laos, which boasts ambitious plans to supply power to south-east Asia in an effort to become the 'battery' of the region.

The elusive giant catfish swims from Cambodia's Tonle Sap Lake up the Mekong to breed in Laos and northern Thailand.

'A fish the size of a Mekong giant catfish simply will not be able to swim across a large barrier like a dam to reach its spawning grounds upstream,' said Roger Mollot, a freshwater biologist for WWF in Laos.

Yet the river plays also host to many unique fish including the vast stingray - the world's biggest freshwater fish - a giant barb and dog-eating catfish, so-called because of its passion for dog carcasses.

'More giant fish live in the Mekong than any other river on earth,' said Dang Thuy Trang, co-ordinator for WWF's Greater Mekong Programme.

'Currently, the lower Mekong remains free-flowing, which presents a rare opportunity for the conservation of these species, but the clock is ticking.'

The plans for the new dam are currently under scrutiny by the Mekong River Commission - an international body made up of Thailand, Laos, Cambodia and Vietnam. But WWF is urging it to veto the plan on the grounds of its effects on the wildlife, fishing and agriculture in the region.