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Nakdong River Mulgeum-Maeri Point Algal Bloom Alert Raised to “Warning” Level… Busan Metropolitan City States, “Tap Water is Safe”

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The Busan Water Authority (hereinafter referred to as the Authority) announced yesterday (August 21) that the Nakdong River Mulgeum-Maeri Point algae alert level had been raised from “Caution” to “Warning.” (Issued by: Nakdong River Basin Environmental Office)

On August 4 and 18, cyanobacteria (hereinafter referred to as algae) cell counts at the Nakdong River Mulgeum-Maeri Point were recorded at 24,439 cells per milliliter (㎖) and 11,802 cells per milliliter (㎖), respectively. As these values exceeded the algae alert warning threshold of 10,000 cells per milliliter (㎖) on two consecutive occasions, the “Warning” level was issued.

• ●Criteria for issuing algae alerts: Cyanobacteria cell counts must meet or exceed the threshold levels for two consecutive measurements.

Alert Level	Cyanobacteria Cell Count (per ㎖)
Caution	1,000 or more
Warning	10,000 or more
Outbreak	1,000,000 or more
Termination	Fewer than 1,000

Since the “Caution” level was first issued at the Mulgeum-Maeri Point on May 29, heavy rainfall in June and July had temporarily eased the situation. However, since August, rising water temperatures and reduced rainfall have created favorable conditions for algal growth, leading to an increase in algae populations and a subsequent upgrade to the “Warning” level. With temperatures forecasted to remain above average in the coming days, algae counts are expected to continue increasing.

< Number of days with algae alerts issued and terminated at the Mulgeum-Maeri Point >

Year	Total Days Issued	Caution / Warning (days)	Issue Date / Termination Date
2020	34	34 / 0	June 18 / July 21
2021	130	104 / 26	June 10 / November 24
2022	196	114 / 82	June 2 / December 14
2023	146	146 / 0	June 15 / December 27
2024	160	119 / 41	June 27 / January 9, 2025
2025	–	–	May 29 / –

In response to the “Warning” level, the Authority is reinforcing water purification measures, including installing algae-blocking curtains and operating spray facilities at intake points to prevent algae inflow, strengthening chlorine and ozone treatments, using high-efficiency coagulants, and shortening the backwashing cycle of sand and activated carbon filters. These efforts aim to ensure safe production of tap water free from algal toxins and odor-causing substances. In addition, two algae removal vessels will be operated near the Mulgeum-Maeri intake point to further minimize algae inflow.

Furthermore, in cooperation with Yangsan City, the Authority is advancing the “Local Metropolitan Waterworks (Intake Facility) Construction Project,” which includes building a multi-level intake tower capable of selective intake at depths of 1m, 5m, and 10m. Once completed, the tower is expected to secure safer raw water sources less affected by algal blooms.

To eliminate public concerns regarding tap water safety, the Authority will also shorten the frequency of analysis for algal toxins and odor-causing substances in both raw and treated water from twice a week to daily, thereby strengthening intake and purification monitoring.

Regarding algal toxins, in addition to the six types of microcystins designated by the Ministry of Environment as monitoring items, the Authority will also test for four additional toxins—anatoxin, nodularin, cylindrospermopsin, and beta-methylaminoalanine (BMAA)—to establish a more rigorous water quality monitoring system.

• ●Hepatotoxins: Microcystin, Nodularin, Cylindrospermopsin

• ●Neurotoxins: Anatoxin, Beta-methylaminoalanine (BMAA)

In particular, algal toxins such as microcystins are completely removed through purification processes (disinfection and activated carbon treatment). There has never been a case of algal toxins being detected in treated water or tap water.

Meanwhile, on August 19, the Ministry of Environment announced a comprehensive reform of the algae alert system, including changes to sampling points, and also stated that it would prepare an integrated countermeasure against algal blooms by the end of the year.
Accordingly, the Mulgeum-Maeri algae alert sampling point will be relocated from 3 kilometers upstream of the Maeri intake plant to a point 50 meters in front of the plant. This change will reduce analysis time from 3.5 days to within 1 day, enabling a “same-day alert system.”
With this reform, the effectiveness of algae countermeasures will be enhanced, allowing intake and purification plants to respond preemptively at the early stages of algal bloom outbreaks, which is expected to significantly alleviate public anxiety.

Kim Byung-gi, Director General of the Busan Water Authority, stated, “Even if algal toxins are partially detected in raw water, they are completely removed by minimizing algae inflow and reinforcing purification processes, so citizens can rest assured that tap water is safe to use.” He added, “The Busan Water Authority provides clean and safe tap water through advanced purification facilities and skilled technical expertise.”