A government investigative commission said Tuesday it found leaks and cracks in six of the 16 dams built on the country’s four major rivers as part of former President Lee Myung-bak’s signature project to refurbish the rivers.

The investigative panel, under the Prime Minister’s Office, said the defects were side effects of flawed construction work. It also said that the project has worsened the water quality in some areas including Nakdonggang River in southeast part of the country.

“An investigation (on the dams) revealed several cracks and leaks at the primary structure of the dams,” the commission said in a briefing held in Seoul. But it added the 16 dams themselves were “structurally safe,” saying they were appropriately designed in consideration of their weight.

It also found erosion in retaining walls and levees at some of the 110 reservoirs around the dams, and advised the authorities to augment the structures.

Prime Minister Chung Hong-won urged all ministries related to the four-river project to cooperate and make sure the necessary steps are taken.

The investigative commission on the four-river project is comprised of civilian experts in engineering, aquatic environment, agriculture and tourism. Since September 2013, it scrutinized the former administration’s flagship project to assess its effects on the environment, agriculture and tourism industries in the region.

The controversial 22 trillion won ($19.95 billion) project has been investigated in light of a series of environmental hazards around the four rivers, such as last year’s algal bloom. Tuesday’s announcement confirmed the link between the project and the algal bloom.

Biochemical oxygen demand ― which is often used as a gauge of water pollution ― has increased in some sections of the Nakdonggang River, indicating that the water quality in the cited section has worsened. The Yeongsangang River has seen an increase in phytoplankton, which seems to have contributed to the surge in algae.

“Dams caused the water to stagnate for too long, which exacerbated the water quality situation,” the commission said. The stagnant water coupled with high temperature appears to have caused the algal bloom in 2013, it added.

The commission did say the project had partial success such as reducing the risk of floods in 93.7 percent of the adjacent regions, although it said the effects fell short of what had been projected in the original plan.

It said most of the problems have been derived from rushing the construction work and the country’s “limited” management of the rivers, and urged the authorities to swiftly mend the leaks while conducting a long-term assessment on the dams’ environmental effects.

Rival parties in parliament showed conflicting reactions over the probe results. Immediately after the announcement, the main opposition New Politics Alliance for Democracy urged a parliamentary investigation on the four-river project, saying the report revealed problems and the need for further investigation.

The ruling Saenuri Party dismissed the call as mere “political wrangling” and said the report showed that the project on the whole had no major problem and just needed minor improvements.

Minor opposition Justice Party, on the other hand, denounced the probe itself, saying the government was merely trying to absolve the “problematic” project.

By Yoon Min-sik (minsikyoon@heraldcorp.com)