The prolonged scorching weather is putting people at risk of not only heat-related illnesses but waterborne diseases as well.

Seoul City has been gripped by a weeks-long heat wave, with the mercury often soaring above 35 degrees Celsius and nighttime highs staying above 25 C, resulting in 13 consecutive tropical nights since July 27.

A total of 89 people have been taken to the hospital for heat-related illnesses such as heatstroke and dehydration since June, whereas 27 people suffered from such illnesses from July to early September last year, according to data compiled by the Seoul Metropolitan Government.

Low precipitation and hot temperatures have also caused algae blooms, which threaten the eco-system in Korea’s major rivers and water supply.

The algae warning issued Thursday in the lower parts of the Han River, the source of drinking water for some 22 million people in Seoul and the surrounding areas, also raises health concerns. The warning had initially been issued only in some upper regions of the river.

Excessive levels of chlorophyll a, a green pigment that indicates the presence of algae, and blue-green algal cells have also been detected in the Nakdong River, which goes through the Gyeonsang provinces and the cities of Busan and Daegu.

When ingested, some types of algae can cause skin or bowel irritation, vomiting, or even liver and nervous system damage in some severe cases. The blue-green scum can also kill fish.

Microcystis is one of the toxic algae. The alga cells produce microcystin, a toxin that can cause liver cancer. The algae can also kill other micro-organisms in the river.

What causes the development and release of this toxin has not yet been figured out, a Seoul City official said.

No deaths linked to the toxic algae have been reported.

Other algae including anabaena, phormidium producing anatoxin ― a toxin benign to humans ― and geosmin, a substance that causes an unpleasant odor.

The Environment Ministry and local governments asked people to be cautious while swimming or doing water activities when an algal advisory or warning is issued.

The ministry also recommends for people to drink tap water only after refrigerating or boiling it.

By Kim Young-won and Yonhap News
(wone0102@heraldcorp.com)