Six of the 16 dams built on the nation's four major rivers have been found to have minor structural problems, a government investigative panel said Tuesday, a discovery that could reignite controversy over their safety.

The investigative commission under the Prime Minister's Office also said the construction of the dams have worsened the water quality of the rivers.

A signature project of the former Lee Myung-bak government, the refurbishment of the Han, Nakdong, Geum and Yeongsan rivers has long been at the center of controversy over allegations of shoddy construction, irreversible environmental damage and collusion in the bidding process for construction contracts.

"After a survey into nine out of the 16 dams, we found water leaks at the (concrete) water receivers of the water pools," the probe team said in a press conference, wrapping up a 16-month investigation. "The dams will need repair work."

The commission also said water quality at some of the rivers has worsened since the 22 trillion won (US$22 billion) project was carried out.

"Dredging and the dams were believed to worsen the water quality by prolonging the time water stays there," the commission noted.

Overall, however, the 16 dams have no serious safety problems, the commission highlighted, adding that, "The 16 dam structures were properly built in consideration of standard weight and the safety level proposed in the design have been attained."

The river project also has successfully lessened the risk of flood in the areas adjacent to the rivers and enabled the use of pooled water for drought-hit areas, the government panel said.

"All in all, the four-river project has attained its goals to some extent ... but it has generated some side effects because it was carried out too hastily amid some limited local river management technology," it said.

The latest probe result came as two rival parties are wrangling over the holding of a parliamentary investigation into the controversial river project.

"(The result) confirmed the pressing need for a parliamentary probe into corruption involving the four rivers," said Park Soo-hyun, spokesman for the main opposition New Politics Alliance for Democracy (NPAD).

"(NPAD) appreciates that the government has admitted to problems after repeatedly denying some safety issues and occurrences of algal blooms."

The ruling Saenuri Party, however, said the four-river project should not be the source of a political feud, calling on the government to come up with measures to address the problems found at the dams.

The country's audit agency earlier confirmed the four-river project to have been riddled with problems in its planning and execution. (Yonhap)