Even though the summer heat has subsided and autumn has arrived, toxic algae blooms continue to persist in the Nakdong River, prompting an environmental organization in Gimhae, South Gyeongsang Province, to call for the opening of the Nakdong River weirs.

According to the Nakdong River Basin Environmental Office on the 22nd, the concentration of harmful blue-green algae cells at the Mulgeum and Maeri sampling points reached 68,039 cells per milliliter (mL) on the 19th. On the same day, 73,818 cells per mL were recorded at the Haman Chilseo point.

These figures are 6.8 times and 7.4 times higher, respectively, than the "Alert" threshold for algae warnings (10,000 cells per mL).

Algae warnings were first issued at both locations in June. Since then, the warning levels have fluctuated, but were upgraded back to "Alert" in August and have remained in effect ever since.

In a statement released that day, the Gimhae Federation for Environmental Movement pointed out, "This demonstrates that algae blooms in the Nakdong River are no longer an issue confined to midsummer. The weirs constructed through the Four Rivers Project have stagnated the river flow, which, combined with high water temperatures driven by the climate crisis, has created an environment highly favorable for algae proliferation."

During a joint survey conducted in August by the Nakdong River Network and the Gimhae Federation for Environmental Movement, the concentration of blue-green algae cells reached 284,000 cells per mL at the Saengnim-myeon water intake facility and 267,000 cells per mL at the Hallim drainage pump station.

At the Saengnim-myeon water intake facility, microcystin—a toxin produced by blue-green algae—was detected at a level of 95.8 nanograms per mL (ng/mL), which is approximately 33 times higher than that of the Hallim drainage pump station (2.9 ng/mL).

The environmental group also argued that the deterioration of water quality in the Nakdong River is leading to an increased financial burden for water purification in Gimhae City.

According to data secured by the group through a public disclosure request, the annual water production of the Samgye and Myeongdong water purification plants surged by about 40%, rising from roughly 48.56 million cubic meters in 2010 to approximately 67.97 million cubic meters last year.

Over the same period, the power costs for operating the purification plants skyrocketed by 274%, from about 2.25 billion won to 8.41 billion won. The power cost per cubic meter of water produced also increased from about 46 won to 124 won.

The organization stated, "While there are other factors at play, such as rising electricity rates and changes in facility operations, and the entire increase cannot be attributed solely to algae treatment costs, it is safe to infer that substantial expenses are indeed going into algae response and riverbank filtration water intake."

They emphasized, "As the burden of water purification grows due to increases in algae and organic matter, the usage of chemicals such as coagulants and activated carbon, along with treatment costs, goes up. Thorough management is also necessary for disinfection byproducts like trihalomethanes, which are generated during the chlorination process."

The group concluded, "Relying on a temporary fix of spending more money to purify water every time an algae bloom occurs is nothing more than a stopgap measure. Gimhae City must formally demand that the central government open the weirs in order to restore the flow of the Nakdong River and reduce algae blooms."

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