Heavy rains could dilute river algae

As up to 120 millimeters (4.7 inches) of rainfall is forecast to fall on parts of the country from yesterday until the end of the day, hope is building that Mother Nature will produce her own antidote to the algal blooms that are polluting Seoul’s Han River and compromising the capital’s supply of drinking water.

When Typhoon Kalmaegi hit Seoul in July 2008, the concentrations of blue-green algae in the river that bisects the capital were severe enough to warrant an advisory warning from the local government. However, the heavy rains it unleashed - up to 200 millimeters - diluted the bacterial microorganisms to contain the problem.

Now the immediate fate of Seoul’s primary water source is hanging in the balance as the weather conditions seem poised to dictate which way the algae will swing.

While heavy rains could dilute it to safe levels, a subsequent burst of sunlight and warm weather could end up making the situation worse by raising the water temperature and providing an ideal breeding ground for the algae.

The Korea Meteorological Administration said yesterday that some central regions, including Seoul, will see more than 100 millimeters of rain by the end of the day. Some southern regions can expect around 30 millimeters of rain for an hour or so, accompanied by thunder and lightning, it added.

The agency said Seoul and its surrounding areas, as well as the Chungcheong regions, will be doused again on Wednesday.

The state-run weather agency expects the mercury to return to normal levels this week, with highs just below 30 degrees Celsius (86 Fahrenheit).

By Kang Jin-kyu [jkkang2@joongang.co.kr]