More than 3 tonnes of fish died after a dam containing contaminated water in Preah Vihear province’s Rovieng district broke during heavy rains on Thursday, said local authorities.

Raksa commune chief Sou Saroeun said about 3 or 4 tonnes of fish died in the Stung Sen River near the commune’s Dounma village.

A group of state engineers began building the small dam in January to block the water so they could construct a bridge, he said.

Dead leaves and plants began to collect and decay behind the dam, contaminating the water, said commune police chief Seoung Soki.

After the dam broke, villagers spotted the dead fish.

“The water at the upper [level] had bubbles. It smelled bad from rotten plants,” Saroeun said.

Villagers collected the dead fish to cook or to make Prahok, a fermented fish paste. None of villagers who ate the fish – including both Saroeun and Soki – became ill.

Chin Monorith, chief of the Rovieng environmental office, confirmed the fish were killed by water contaminated by rotting vegetation.

“The incident was not caused by any [man-made] poison,” he said.