Mass fish deaths have been reported in the upstream area of Soyeong Lake in Gangwon Province, South Korea.
The incident has sparked a dispute between government researchers and local fishermen over whether the lake bottom is contaminated with toxic gases. This conflict highlights the potential ecological risks associated with long-term damming and the accumulation of organic waste.
Local fishermen and some investigators suspect that the lake bottom is filled with hydrogen sulfide [1]. They believe that 50 years of dam blockage [1] allowed pig and cow manure, along with pesticide-contaminated runoff, to accumulate. This process is thought to have created anaerobic conditions that generate the toxic gas, leading to the die-offs [1], [2].
However, official findings contradict these claims. The Gangwon-do Health & Environment Research Institute said the water-quality rating was "very good" [1]. The institute said that no harmful substances were detected during its testing [1].
Despite the official rating, a testing team commissioned by the fishermen reported different results. The team said that contamination in the lake-bottom sediment was severe [1].
Government officials have taken note of the situation. President Lee Jae-myung and Minister of Climate and Energy Kim Sung-hwan discussed the reports of dying crucian carp in the Soyeong River [1]. The Fisheries Disease Control Agency is also involved in the ongoing investigation to determine the exact cause of the mortality event.
Investigators are now attempting to reconcile the gap between the surface water quality and the condition of the sediment layers at the bottom of the lake [1], [2].
“The lake bottom is reported to be filled with hydrogen sulfide after 50 years of dam blockage.”
The discrepancy between surface water tests and sediment analysis suggests a stratified environmental crisis. While the upper water column may appear healthy, the accumulation of organic matter over five decades can create a 'dead zone' of hydrogen sulfide at the bottom. If these anaerobic layers are disturbed or expand, they can cause sudden, large-scale fish kills regardless of the overall water-quality grade.
