The government on the 9th announced an investigation finding that oxygen shortage in the lower layer of the lake caused the mass die-off of crucian carp in the upper reaches of Soyang Lake in Gangwon Province. The Ministry of Climate, Energy and Environment said it will strengthen support for managing organic discharges in the upper reaches of Soyang Lake, identified as the cause, and expand support programs for fishers who suffered damage. On Apr. , crucian carp, carp, and eels died en masse in the upper reaches of Soyang Lake, forcing 49 nearby fishing households to halt operations.
The ministry said that through an investigation led by the National Institute of Environmental Research, it confirmed oxygen-deficient (low-oxygen) conditions at some points as oxygen was consumed during the decomposition of organic matter in the lower layer of Soyang Lake. It added that high water levels and temperatures in spring and low rainfall prevented mixing of the lake's surface and bottom layers, exacerbating oxygen depletion.
It also analyzed that infections with bacteria, as immunity dropped during the April spawning season, had an impact. It judged that hydrogen sulfide in the water, which had been cited as a cause, did not directly affect the die-off. That is because hydrogen sulfide was not detected in the water, and only trace amounts of 0.003–0.022 mg per liter were found among bottom sediments. The Fisheries Research Center affiliated with the Environmental Research Institute at Kangwon National University noted in a report last month that hydrogen sulfide poisoning was one of the causes of the die-off.
To help fishers recover from damage, the government will provide fishing materials such as gear and nets at half price and expand existing support programs for fishing households, including purchasing ecosystem-disrupting species. Korea Water Resources Corporation (K-water), the manager of Soyang Lake, will support the creation of crucian carp spawning grounds to resume fishing.
To prevent organic matter from accumulating, the government will promote crop conversion and the creation of terraced fields for highland fields in the upper reaches of Soyang Lake. Public authorities will take over livestock manure treatment previously handled by individuals. Sediments near the 38 Bridge, where organic concentrations were high, will also be removed. It plans to monitor to detect oxygen shortages in the lake's lower layer in advance and operate water-circulation devices.