Algal blooms have begun to spread across Daecheong Lake, a vital source of drinking water for the Chungcheong region, earlier than in previous years.

The waters near Hwanpyeong and Chuso-ri in Gunbuk-myeon, Okcheon-gun, North Chungcheong Province—often cited as the "epicenter of algal blooms" where green streaks first appear each year—are already stained a deep green. Dark brown algal scum, which emits a foul odor, can also be seen floating on the surface.

According to local residents on Friday (June 26), the algal bloom started earlier than usual due to spring droughts and early heat, and is now spreading toward the center of the lake.

In some areas, thick, viscous clumps of algae have washed ashore, creating patches that look as if deep green paint has been spilled and is now decaying.

Park, a 70-year-old resident, explained, "The water surface began turning deep green early this month, and as time passes, the water is becoming so murky that it is impossible to see even an inch ahead."

This area, where the So-okcheon stream—a tributary of the Geum River—flows in, has little water flow and shallow depths, making it a habitual site for high-density algal blooms.

Typically, the green tint begins to intensify around the monsoon season and spreads to surrounding areas as water temperatures rise.

"To protect the quality of our drinking water, we must act quickly before the monsoon season to remove the algal scum and pollutants lingering along the edges," Park said.

Algal blooms occur when nutrients such as nitrogen and phosphorus from land are washed into the water by rain, followed by the proliferation of harmful cyanobacteria due to rising water temperatures.

Cyanobacteria, a type of phytoplankton, are an essential component of the aquatic ecosystem. However, excessive growth can cause foul odors, degrade water quality, and even lead to fish die-offs.

Since the construction of the dam, Daecheong Lake has experienced recurring algal blooms like an annual event.

Since the implementation of the algal bloom alert system, alerts have been issued almost without exception between summer and autumn; last year, an alert remained in effect for 139 days.

The situation has become so common that the term "algae latte" has emerged to describe the lake, which turns deep green every summer.

With the early onset of the blooms, the Korea Water Resources Corporation (K-water), the managing authority, is on high alert regarding water quality management.

The K-water Daecheong Dam branch is currently operating five algal bloom containment barriers, 33 underwater aeration devices (air supply systems), and 36 water circulators at full capacity to prevent the spread of algae. They have also deployed one algae removal vessel to collect algal scum.

A K-water official stated, "We are strengthening our monitoring of algal blooms and collecting pollutants around the lake to reduce the inflow of contaminants during the monsoon season," adding, "We are also considering leasing and deploying three additional algae removal vessels."

(Photo: Yonhap News)