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Algae Alert Raised to “Warning” Level at the Mulgeum–Maeri Section of the Nakdong River… Busan Metropolitan City Assures Residents That Tap Water Remains Safe

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The Busan Water Authority announced today (June 22) that the algae alert at the Mulgeum–Maeri section of the Nakdong River has been raised from the “Caution” level to the “Warning” level. The alert was issued by the Commissioner of the Nakdong River Basin Environmental Office.

According to monitoring results, harmful cyanobacteria cell counts at the Mulgeum–Maeri section reached 21,868 cells per milliliter (mL) on June 15 and 13,288 cells per milliliter on June 22. Because the count exceeded the “Warning” threshold of 10,000 cells per milliliter on two consecutive occasions, a “Warning” alert was issued.

The criteria for issuing algae alerts are based on harmful cyanobacteria cell counts meeting the threshold for a particular alert level on two consecutive monitoring occasions.

Alert Criteria

Caution: 1,000 cells/mL or more

Warning: 10,000 cells/mL or more

Bloom Outbreak: 1,000,000 cells/mL or more

Cancellation: Less than 1,000 cells/mL

Since a “Caution” alert was first issued for the Mulgeum–Maeri section on June 8, prolonged high temperatures and exceptionally low rainfall have created favorable conditions for algal growth. As a result, algae populations increased rapidly, leading to the escalation to the “Warning” level after just two weeks. Temperatures are forecast to remain above seasonal averages in the coming period, and algae populations are expected to continue increasing.

In response to the issuance of the “Warning” alert, the Busan Water Authority has strengthened its treatment processes to prevent algae from entering the water supply and to ensure the production of safe drinking water free from algal toxins and odor-causing substances. Measures include installing algae barriers at intake facilities, operating water-spraying systems, increasing chlorine and ozone treatment, using high-efficiency coagulants, shortening backwashing cycles for sand and activated-carbon filters, and adding powdered activated carbon. The Authority also plans to operate algae-removal vessels near the Mulgeum and Maeri intake points to minimize algal inflow.

In addition, through the Regional Wide-Area Water Supply (Intake Facility) Construction Project being carried out jointly with Yangsan City, a new intake tower capable of selective water withdrawal at depths of 1, 5, and 10 meters is currently under construction. Once completed, the facility is expected to secure safer source water that is less affected by algal blooms.

To further address public concerns regarding drinking water safety, the Authority will strengthen source-water surveillance and treated-water monitoring by increasing the frequency of analyses for algal toxins and odor-causing substances in both raw water and treated water from twice per week to daily testing.

Regarding algal toxins, the Authority is expanding its monitoring program beyond the six types of microcystins designated by the Ministry of Environment. Four additional toxins—anatoxin, nodularin, cylindrospermopsin, and beta-methylamino-L-alanine (BMAA)—will also be analyzed to provide more comprehensive water quality surveillance.

In terms of toxicity categories, microcystins, nodularin, and cylindrospermopsin are liver toxins, while anatoxin and beta-methylamino-L-alanine (BMAA) are neurotoxins.

The Authority emphasized that algal toxins, including microcystins, are completely removed through the water treatment process, particularly during disinfection and activated-carbon treatment stages. To date, there has never been a case in which algal toxins were detected in treated water or tap water.

Kim Byung-gi, Director of the Busan Water Authority, stated, “Even when severe algal blooms occur in the Nakdong River, algal toxins and odor-causing substances can be completely removed through measures that minimize algal inflow and strengthen water treatment processes. Residents can therefore use tap water with confidence.”

He added, “The Busan Water Authority continues to provide clean and safe drinking water through advanced water treatment facilities and highly skilled technical expertise.”