An algae outbreak has been spreading throughout the country. Authorities said on Thursday that the outbreak has reached the upper part of the Nakdong River in the southern region since starting in the lower stretch in June and contaminating the middle part in July. They also issued the first algae alert for the Han River since 2008, as well as one for Paldang Lake in Gyeonggi Province on July 27.
As concerns mount over the safety of drinking water, there is growing controversy over the cause of the phenomenon. Environmental groups hold the government's four-rivers mega project responsible, saying it has slowed the natural flow of the rivers, while the government blames the heat wave and lack of rainfall.
Experts say algae outbreaks are caused by high water temperatures, strong sunlight and the amount of phosphorous in the water, which is their basic source of food. Other important factors are flow speed and depth.
The government claims that the creation of weirs on the four major rivers of Korea would in fact increase the amount of water flowing through them and help clean up the water. But opponents of the project say the increase in amount of water could slow down its flow and worsen its quality.
"There was a lot of rain until the middle of last month causing the amount of water in rivers to rise," said Kim Jwa-kwan at Catholic University of Pusan, a critic of the project. "The average temperature in July was only 0.4 degree Celsius higher than last year. The latest algae outbreak is due to the slowdown in the flow of water."
But a government official said, "Algae outbreaks are a natural occurrence when water flow slows down, but there was an unusually small amount of rain this summer and strong sunshine. Those are the main reasons for the outbreak."