Environment protection advocates have raised a new claim that the four-river refurbishment project, led by former President Lee Myung-bak, has undermined water quality.
They recently cited bryozoans, known as moss animals, which were found to have formed colonies in the nation's four largest rivers ― Hangang, Geumgang, Yeongsangang and Nakdonggang ― as evidence that the rivers' ecological systems have suffered from the project.
A moss animal is a 0.5-millimeter-long aquatic invertebrate that generally lives in brackish water.
"Bryozoans (called pectinatella magnifica among scholars) do not usually inhabit flowing waters. As the water flow has been slowed by the refurbishment project, they appear to have formed in various regions along the four major rivers," said Lim Hee-ja, a spokeswoman for the Masan-Jinhae-Changwon environmental group association.
"Like occurrences of algal blooms, or green tides, detection of the moss animal means that some regions of the rivers are contaminated," said Jung Soo-geun, a leader of the Daegu district environment protection gathering.
The Ministry of Environment downplayed the possibility. It claimed that the species lived not only in contaminated areas but also in clean water. It stressed that the moss animal was not harmful to humans.
But the ministry added it would closely collaborate with nongovernmental environment advocates to continuously monitor the situation.
Environment groups said it is necessary for the National Assembly to carry out a full-fledged investigation into the Lee administration-initiated 22 trillion won ($21.7 billion) four-river project.
They claimed that all refurbishment construction should be halted as soon as possible to prevent further damage to the ecosystem.
Some ruling and opposition lawmakers have already raised concerns about worsening water quality and environmental damage in the nation's four major rivers after a massive project of dredging, damming and straightening up the waterways.
"Since the river development, 28 legally protected animal species have disappeared from the four major rivers," said Rep. Jang Ha-na of the main opposition New Politics Alliance for Democracy, citing a report from the Ministry of Environment.
Jang said the report found that endangered species and natural monuments such as the stork, golden eagle and sea eagle spoonbill have disappeared because of the massive restoration project.
Rep. Yi Wan-young from the ruling Saenuri Party said that the country spent 9.3 trillion won from 1999 to 2012 for water improvement in the Nakdonggang River, but the water quality remains low, only being suitable for industrial use.