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Water Bloom Alert Issued at the Mulgeum–Maeri Site for the First Time This Year at the “Attention” Level… Busan Metropolitan City Ensures Safe Tap Water Supply Through Thorough Water Treatment

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Busan Metropolitan City, led by Mayor Park Heong-joon, announced today (June 8) that the first Water Bloom Alert of the year has been issued at the “Attention” level for the Mulgeum–Maeri section of the lower Nakdong River. The alert was issued by the Nakdong River Basin Environmental Office.

The alert was issued after surveys conducted by the Ministry of Climate, Energy and Environment (National Institute of Environmental Research) on June 1 and June 8 found algae cell counts of 2,418 cells/mL and 8,458 cells/mL, respectively, at the Mulgeum–Maeri site. These measurements exceeded the “Attention” alert threshold of 1,000 cells/mL on two consecutive occasions.

The City believes that harmful cyanobacteria have increased due to the continued presence of environmental conditions favorable to algal growth, including elevated water temperatures and increased sunshine. This year’s alert was issued 10 days later than last year.

According to the Korea Meteorological Administration, temperatures are expected to remain at or above seasonal averages for the foreseeable future, and algae cell counts are therefore expected to continue increasing.

To enable more proactive responses from the early stages of algal proliferation, Busan Metropolitan City has, since August 2025, relocated the Mulgeum–Maeri sampling point from 3 kilometers upstream of the Maeri Intake Station to a location 50 meters in front of the intake facility and has been operating an immediate same-day alert issuance system.

In addition, the City is operating a seasonal algae management program from May 15 to October 15, intensively monitoring algae conditions. Beginning in late July, when algae growth is expected to accelerate significantly, algae removal vessels will be deployed around the intake area at the Mulgeum–Maeri site to collect and remove algae directly on-site.

Following the issuance of the “Attention” level alert, Busan Metropolitan City is also strengthening source water surveillance and water treatment measures to ensure a safe drinking water supply for residents.

Algae cell counts at the Mulgeum–Maeri site are being monitored daily. In addition, the City independently conducts phased testing for nine algal toxins and two odor-causing compounds, twice weekly during the “Attention” stage and daily during the “Warning” stage.

Even when algae are detected in source water, the City removes algal toxins and odor-causing substances by enhancing treatment processes, including chlorine and ozone treatment, the use of high-efficiency coagulants, and more frequent backwashing of sand and activated carbon filters.

The City also plans to fundamentally prevent the inflow of harmful cyanobacteria by installing a selective-depth intake tower near the Mulgeum Intake Station by 2028, enabling water withdrawal from different depths.

Furthermore, Busan Metropolitan City will continue operating its pilot algae alert program for waterfront recreation areas at Samnak and Hwamyeong Leisure Sports Towns to ensure public safety during recreational water activities.

In particular, beginning this year, a strengthened algae alert system that considers both cyanobacteria cell counts and algal toxin concentrations will be implemented.

If algal toxin concentrations exceed 20 micrograms per liter (μg/L), a “Warning” level alert will be issued, and recommendations will be made to prohibit waterfront activities such as fishing, swimming, and water sports, thereby enhancing public safety management.

Lee Byung-seok, Assistant Mayor of Environmental Water Policy Office, stated, “To minimize algal inflow at the Mulgeum–Maeri site, which serves as Busan’s water intake source, we are operating algae barriers and spray facilities while also strengthening treatment processes at our water treatment plants. We are doing our utmost to ensure that residents can continue to use clean and safe tap water.”