By Kim Rahn

Seoul City has issued an algae advisory as the upper streams of the Han River, which is the source of drinking water for 25 million people in the capital area, have seen algae blooms.

This is the first advisory since 2008 and sixth since 2000.

The Seoul Metropolitan Government issued the advisory at 2 p.m. for the upper reaches of the river between Gangdong Bridge and Jamsil Bridge, as the blooms have spread fast because of the high water temperature and a lack of rain following the weeks-long heat.

“The levels of algae exceeded the advisory standards in two consecutive tests conducted on Aug. 1 and 8, respectively,” a city official said.

The concentration level of chlorophyll-a, an index of algal biomass, was 14.3 to 34.2 milligrams per cubic meter at five locations of the upstream section, surpassing the advisory level of 15. Between 1,180 and 4,470 cells per milliliter of blue-green algae were also detected, far more than the advisory level of 500 cells.

The algae advisory is placed when such high levels of chlorophyll-a and blue-green algae are detected in two tests conducted at an interval of a week. In the first test conducted on Aug. 1, the level for chlorophyll-a was between 12.8 and 27.4 milligrams and that for blue-green algae, between 240 and 820 cells.

The official said the test results on whether the water contains toxins will come out today. In a previous test, the city detected a small level of microcystis, a type of blue-green algae, which can produce toxin causing liver diseases, but said no such toxin was found this time.

“It’s not a worrisome situation and the waterworks facilities filter the water to a safe level. The algae contain geosmin, a compound causing earthy odor, but the filtering process lowers its level below the Ministry of Environment standard for drinkable water. We haven’t had complaints from citizens about bad smells in tap water,” the official said.

“Without a large amount of rainfall or typhoon, the contamination may continue. The algae concentration levels in the lower reaches of the river also surpassed the advisory levels in the test on Tuesday, and we may issue the advisory for the section, too, following a second test next Tuesday.”

In the meantime, some experts claimed the Lee Myung-bak administration’s four-river refurbishment project is to blame for the algal bloom.

During a forum in Seoul, prof. Kim Jwa-kwan of Catholic University of Pusan said reservoirs set up as part of the projects make the flow of the rivers slower, helping algae spread fast.

He said the government has built eutrophication-prevention facilities but claimed they can’t prevent algae contamination. “For now, the most effective way to control algal bloom is opening the sluices of the 16 reservoirs in the four rivers,” Kim said.