Hundreds of kilograms of dead fish have washed up on the shores of the Mekong in Stung Treng’s Thala Barivat district in the past month, and while environmental activists blame construction of the controversial Don Sahong dam upstream, officials yesterday said the fish are being “poisoned” by Lao fishermen.

“We saw that a lot of dead fish flowed from the upper Mekong in Lao,” said O’Svay commune chief Roth Sun, who believes the fish were poisoned near the border.

Villagers have collected some 400 to 500 kilograms of fish, and several fell ill from eating them, Sun said, adding that commune authorities found cooked rice with a “blue substance” inside the fish bodies, prompting them to warn villagers against eating the fish.

Sim Kosal, 23, from nearby Preah Romkil commune suspects the Don Sahong construction is to blame, a viewed shared by activists.

“Fish have died since the construction started . . . [and] the water quality is worse than last year,” he said.

Pen Chhundy, provincial Fishery Administration director, yesterday was unaware of the deaths but said that an inspection following fish deaths in the district last month found that illegal poison-based fishing practices by Laotians were to blame.

NGO Forum executive director Tek Vannara said the dam construction’s impact on water quality is likely the cause of not just the fish deaths but also the death of two Irrawaddy dolphins this year and possibly the deaths of some 355 cattle in Stung Treng since April. “We must investigate,” he said.

Additional reporting by Alessandro Marazzi Sassoon