Preliminary findings from a soon-to-be released comprehensive report have reinforced dismal projections for the future of Cambodia’s fisheries if 11 planned mainstream hydropower dams are built on the Mekong River.

Presented yesterday on the first day of the Greater Mekong Forum on Water, Food and Energy in Phnom Penh, the impact assessment projected more than half of fish catches in regions connected to the Mekong could be lost if the dams – nine in Laos and two in Cambodia – are established in the coming decades.

The blocking of fish migratory pathways and a 50 per cent drop in water nutrient levels caused by the trapping of sediment were noted among the major threats to fish and aquatic life posed by the proposed plants.

Researcher Ian Cowx, director of the International Fisheries Institute at Britain’s Hull University, said the dam could wipe out 100 per cent of fish that migrate long distances.

He said there was no such thing as “fish friendly turbines”, and that reservoirs would stop larvae from drifting downstream, which there is “no technological method to overcome”.

“When you have 11 dams there ain’t a lot left when you get to the bottom” of the stream, Cowx said.

Commissioned by the Vietnam National Mekong River Committee and undertaken by water environment consultancy DHI, the two-and-a-half-year study – set for release in December – focused on the environmental, social and economic impact on the Kingdom’s floodplains, the Mekong Delta in Vietnam and the Tonle Sap lake.

Baseline data calculated that fish production in those regions was about 500,000 tonnes for Cambodia and 700,000 tonnes for Vietnam.

If all the hydropower plants go ahead, according to Cowx, “the bottom line is that we have estimated we will lose about 360 to 370 thousand tonnes of fish and aquatic organisms in Vietnam and about 270,000 tonnes in Cambodia.”

Citing its need for cheap electricity to develop its economy, Laos has pushed ahead with its hydro plans.

The Xayaburi dam in the north of the country is under construction while work on the planned Don Sahong hydropower plant 2 kilometres north of Cambodia’s border is slated to begin soon.

A previous study by the Mekong River Commission, which used data from 2000, found the Lower Mekong Basin would lose between 550,000 to 800,000 tonnes, or 26 per cent to 42 per cent, of fish resources, because of planned hydropower development on the Mekong.