Seoul Mayor Park Won-soon on Monday jumped into the debate over the cause of a recent algae outbreak in major rivers, blaming President Lee Myung-bak’s four rivers pet project as the main culprit.

Blue-green algae blooms have covered the upper stream of Han River, the source of drinking water for 25 million people in greater Seoul, prompting city officials to issue an algae crisis advisory.

“Han River is now more like a lake, with weirs blocking water flows,” the mayor said in a radio interview. Park is a long-time civic activist and a member of the main opposition Democratic United Party.

“The main cause of the green algae phenomenon, I think, is the dams and wires in the North Han River.”

His remarks echoed arguments by environmentalists and some scientists who claim that the weirs and mini-dams built as part of the controversial river redevelopment project have slowed water flows, creating an environment where algae can grow thick.

The government, however, claims that a record-setting heat wave, coupled with a prolonged drought, was the main reason behind the phenomenon.

Experts, while noting that there are many contributing factors to an algae outbreak, are divided over whether the massive river dredging and damming work contributed to the unprecedented level of algae growth, and if so, to what degree.

A presidential campaign pledge of Lee, who proviously an the nation’s largest construction firm, the 22 trillion won four-river project has been highly controversial from its inception four years ago up until now when 98 percent of work is completed.

The government claims it is a pre-emptive approach to better manage the nation’s water resources and protect the environment, while environmentalists call it a typical case of “green camouflage,” accusing the Lee administration of disguising an anti-environmental, massive development work as a green project.

Meanwhile, the density of algae in Nakdong and other rivers appeared reduced after heavy rains on Sunday, although experts warned it may be only a brief respite and that algae blooms may spread again once dry, hot weather returns.

Major dams and weirs in affected rivers have been releasing water since Friday, as part of the government’s measures to combat the spread of blue-green algae.

By Lee Sun-young (milaya@heraldcorp.com)