"The algal bloom that started a month ago has reached its worst phase as we entered the rainy season. It is hard to see even a hand's span into the water, and with a strong rotting smell filling the air, it is even difficult to breathe," said Park, a 70-year-old resident who was removing wild cucumbers (an invasive plant) in Jiori, Gunbuk-myeon, Okcheon-gun, North Chungcheong Province, yesterday (July 23), describing the severe algal bloom turning Lake Daecheong a deep green as the "worst ever."

This is because the algal blooms, which started earlier than usual due to spring droughts and early heatwaves, spread to surrounding lakes and are now forming dark brown clumps that are rotting amid hot and humid weather.

"The water is filled with dense algal debris up to a depth of 1 meter," Park added. "Algal blooms in Lake Daecheong repeat like an annual event, but it has never been this severe."

This area, where the Sogokcheon stream, a tributary of the Geumgang River, flows in, is called the epicenter of Lake Daecheong's algal blooms due to its shallow water and stagnant flow.

Every year, green ribbons starting from this area tend to spread toward the center of the lake.

This year, along with the monsoon rains, the algal blooms here are spreading across the entire lake.

An algal alert "warning" stage was issued for the Hoenam water area (Boeun) as of the 20th, and conditions are also worsening in the Muni (Cheongju) and Chudong (Daejeon) water areas.

"If we had quickly scooped up the algal debris starting from the edges of the lake like Jiori, we could have avoided the worst situation we are facing now," Park said. "Removing the rotting algal debris at the edges is urgent even now."

Algal blooms occur when nutrients such as nitrogen and phosphorus from land are washed in by rainwater, followed by a rise in water temperature that causes harmful cyanobacteria to proliferate.

Cyanobacteria, a type of phytoplankton, are an essential component of the aquatic ecosystem, but when excessively proliferated, they cause bad odors, deteriorate water quality, and sometimes lead to fish kills.

Algal blooms have repeated like an annual event in Lake Daecheong since the dam was built.

Since the implementation of the algal warning system, alerts have been issued almost without exception between summer and autumn, and last year, the alert continued for 139 days.

As the algal bloom situation worsens, the Korea Water Resources Corporation (K-water), the management authority, is also strengthening water quality management.

To prevent the spread of algal blooms, the corporation is fully operating five algal blocking curtains, 33 underwater aeration facilities (air supply devices), 36 surface aerators (water circulation devices), and has deployed four algal removal boats to scoop up the debris.

(Photo provided by reader, Yonhap News)