Crucian Carp Mass Die-Off During Spawning Season in Soyang Lake Devastates Fishermen... Is Hydrogen Sulfide the Cause?

Mass Die-Off of Crucian Carp, Carp, and Eels

Hydrogen Sulfide Poisoning Suspected Due to Sediment Pollution

A mass die-off of crucian carp has occurred upstream of Soyang Lake in Inje County, Gangwon Province, causing damage to local fishermen. Photo by Yonhap News

Since early April, a mass die-off of crucian carp has occurred in the upper reaches of Soyang Lake in Inje County, Gangwon Province, resulting in local inland fishermen being unable to fish for crucian carp for over a month and suffering significant losses.

According to Inje County officials on May 17, mass deaths of crucian carp, carp, and eels have continued since early April in the areas of Bupyeong-ri, Gwandae-ri, and Sinwol-ri, which are located in the upper reaches of Soyang Lake.

The main fishing season for crucian carp typically lasts from late March until the acacia trees bloom. However, this year, crucian carp that migrated upstream for spawning have died before even being able to spawn, leading fishermen to effectively halt their operations.

The losses suffered by the fishermen are significant. On average, a single fisherman using a basket net can catch about 900 kilograms of crucian carp in a week. Given that crucian carp are traded at 5,000 won per kilogram, over a six-week period, each fisherman has lost approximately 30 million won in income.

Considering that there are a total of 49 fishermen whose livelihoods depend on Soyang Lake, the overall estimated losses exceed 1 billion won.

The problem is not limited to crucian carp. Other fish species have also been affected, further increasing the damage to fishermen. So far, over 2 tons of adult crucian carp, carp, and eels have died. In terms of the number of fish, this amounts to tens of thousands.

The Fish Research Center, affiliated with the Institute of Environmental Studies at Kangwon National University and commissioned by the Nam-myeon Fishery Association, identified “hydrogen sulfide (H2S) poisoning and other complex environmental stresses” as the causes of the fish kill.

Hydrogen sulfide was detected in water samples at concentrations as high as 519 micrograms per liter (ug/L). Considering that the lethal concentration at which half of the fish die after 96 hours of exposure is 5 ug/L, the detected level is as much as 104 times higher than this threshold.

The research team determined that large amounts of organic matter accumulated on the lakebed were decomposed, generating high concentrations of hydrogen sulfide in the bottom water. With the rise in water temperature in spring, the hydrogen sulfide generated damaged and paralyzed the respiratory organs of crucian carp and carp, which was identified as the direct cause of death.

In addition, the research team diagnosed that the water body had become eutrophic due to high concentrations of phosphate phosphorus, and that the resulting excessive algal blooms and oxygen deficiency further deteriorated the habitat for fish.

Previously, Inje County had notified the Gangwon Institute of Health and Environment about the mass die-off of crucian carp and requested a water quality inspection, but the cause could not be determined. This is because hydrogen sulfide is not included among the parameters for water quality inspections by administrative agencies. In other words, Soyang Lake meets standard water quality indicators, but the environment is not suitable for fish to survive.

Upon hearing the news, President Lee Jaemyung ordered Minister of Climate, Energy and Environment Kim Sunghwan to review the cause at a Cabinet meeting on May 12. On May 15, Minister Kim visited the upstream site of Soyang Lake to discuss detailed investigations and countermeasures with fishermen and relevant organizations. In connection with this, Minister Kim stated, "We will conduct another precise analysis of the cause within two weeks." The government is expected to prepare and implement countermeasures as early as early June.

This content was produced with the assistance of AI translation services.