BUSAN (Yonhap News) ― Green algae blooms in one of the country’s four major rivers have worsened following the completion of a controversial refurbishment project by the previous administration, a local environment group claimed Wednesday.

The administration of former President Lee Myung-bak carried out the 22.2 trillion won ($19.8 billion) project aimed at enhancing the nation’s water management system as well as preventing flooding in the four rivers ― the Hangang, Nakdonggang, Geumgang and Yeongsangang.

But the mega-budget project has been at the center of controversy over its possible adverse effects on the environment and mounting burdens on the state budget.

The environment group based in the southern port city of Busan said at a press conference that green algae blooms have spread to the entire Nakdonggang River, which stretches along the southern part of the country.

“The Nakdonggang River has transformed into an enormous polluted river in just about one year,” the group said. “The phenomenon poses serious health threats to local residents.”

The group argued that weirs built across the river have turned parts of the rivers into standing water, an ideal breeding ground for bacteria that create algal blooms.

A weir is a low barrier that is built across a river in order to strengthen riverbeds and to control or direct the flow of water.

The environmentalists further claimed that the weirs have worsened the algae bloom phenomenon by slowing down river flows too much and thus should be torn down in the long-term.