Algal blooms are currently choking up several rivers in South Korea. Environmentalists blame The Four Major Rivers Restoration Project, which was completed last October at a cost of 22 trillion won (US$19+ billion), for this. The algal bloom covers the Han, Geum, Nakdong, and Yeongsan rivers. The project built 16 dams and dredged up 520 million cubic meters of mud from the river beds to make flood prevention simpler.
The dams have turned part of the rivers into standing water, which is an ideal breeding ground for the cyanobacteria making up algal blooms. The blooms appeared last winter, which was unusual, and reappeared this summer, causing a major scare over the quality of the country’s drinking water. The algae are affecting the Nakdong and Han more seriously, which supply water to more than 10 million people living in Seoul and the surrounding areas.
The severity of the blooms has been so severe that Seoul’s metropolitan government is advising residents to boil any tap water intended for drinking. Sales of bottled water have soared. The South Korean government maintains that the dams aren’t to blame and that the blooms are caused by the year’s unusually long heat wave and associated drought.
It’s possible that plenty of sunlight with high levels of nutrients in the rivers is responsible for the algal outbreak. Since algae don’t thrive in waters deeper than 3 meters, the dams and deep reservoirs should have curbed algal growth but they haven’t.
Recently the blooms have been receding as heavy rains have been dissipating the algae.