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First “Caution” Level Algae Alert Issued This Year at Nakdong River’s Mulgeum and Maeri Points – Busan City Mobilizes All Efforts to Ensure Safe Tap Water Supply

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Busan Metropolitan City (Mayor Park Heong-joon) announced today (May 29) that the first “Caution” level algae alert of the year was issued at the lower Nakdong River’s Mulgeum and Maeri points. (Issued by: Nakdong River Basin Environmental Office)

Algae cell concentrations measured on May 19 and 26 were 1,267 and 5,984 cells/mL respectively, exceeding the caution level threshold of 1,000 cells/mL for two consecutive measurements—thus meeting the criteria for issuing the alert.

High water temperatures and increased sunlight have continued to create favorable conditions for the growth of harmful cyanobacteria (hereinafter “algae”). While last year’s first caution-level alert was issued on June 27, this year’s alert has come nearly a month earlier.

According to the Korea Meteorological Administration’s mid-term forecast, daytime temperatures are expected to remain near seasonal averages (23–29°C) with no rainfall expected, indicating a continued rise in algae populations.

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Algae Alert Issuance Criteria

Level	Cell Count (cells/mL)	Algae Toxins (Microcystins)
Caution	1,000 or more (2×)	-
Warning	10,000 or more (2×)	10 µg/L or more
Bloom	1,000,000 or more (2×)	-
Release	Below 1,000	-

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In response to the alert, the city is implementing the following actions to ensure safe drinking water:
▲ Blocking algae inflow at water intake and purification plants (installation of barriers, activation of sprinklers)
▲ Strengthened monitoring of raw and purified water
▲ Enhanced water purification processes

In addition, algae removal vessels will be deployed at Mulgeum and Maeri starting in July to proactively address potential blooms.

The city is currently conducting daily algae cell count tests at the intake sites and also tests for 9 types of algae toxins and 2 odor compounds.
Testing frequency:

• ●“Caution” level: twice weekly

• ●“Warning” level: daily

Even when algae are detected in raw water, advanced purification measures—such as chlorine disinfection, high-efficiency coagulants, and increased backwashing frequency of sand and activated carbon filters—are effective in completely removing toxins and odors. Tap water remains safe for consumption.

Construction of an intake tower with selective depth withdrawal capability is underway and is expected to be completed by 2027.

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Extension of Recreational Area Algae Alert Trial Operation

The city will extend the trial operation of the recreational area algae alert system—initiated in June 2024 at Samrak and Hwamyeong Leports Town—through December 2025.

Starting this year, the criteria for issuing alerts in recreational zones have been strengthened. A single measurement exceeding 500,000 cells/mL will immediately trigger a “Warning” level alert, leading to restricted access to water-based recreational activities.

Level	Cell Count (cells/mL)	Criteria Type
Caution	20,000 or more (2×)	Existing
Warning	100,000 or more (2×) OR 500,000 or more (1×)	Reinforced
Release	Below 20,000

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Mayor Park Heong-joon stated:
“To minimize algae inflow into our city’s water intake points at Mulgeum and Maeri, we have installed algae barriers, activated spray facilities, and are operating reinforced purification processes at our water treatment plants.
We will do everything we can to ensure that citizens can continue to enjoy clean and safe tap water.”