Algal bloom

The Nakdong River, South Korea's longest at 510 kilometers, has been blanketed by severe algal blooms fueled by persistent extreme heat.

Daegu’s Dalseong County issued a caution level algae warning Friday after blooms appeared in the Nakdong River near the Gangjeong Goryeong Weir, where algae removal boats are now in operation.

According to the Ministry of Environment’s three-tier algae alert system, a caution warning — the middle level — is issued if chlorophyll-a concentrations exceed 25 milligrams per cubic meter in two rounds of water quality tests conducted two weeks apart.

The lowest tier, an advisory, is triggered at 15 milligrams per cubic meter, while the highest level, an alert, is declared at 100 milligrams per cubic meter.

Green algae blooms typically result from a mix of high water temperatures, nutrient pollution and stagnant water, conditions which often worsen during summer.

Haman County in South Gyeongsang Province, located in the lower reaches of the Nakdong River, was also placed under a caution algae warning Thursday.

“Across the Nakdong River, algal blooms have grown more severe as the prolonged heat wave continues. We plan to put up additional banners advising residents living near the river to refrain from fishing, swimming, harvesting or consuming shellfish," said an official from the Nakdong River Basin Environmental Office under the Environment Ministry.

Earlier in the day, showers fell in Greater Seoul — encompassing the capital, Incheon and Gyeonggi Province — parts of Gangwon Province, the Chungcheong and Jeolla provinces, and Jeju Island. However, most areas still saw high temperatures ranging between 30 and 35 degrees Celsius, according to the Korea Meteorological Administration.

The KMA forecast frequent showers and continued sweltering heat through next week.