YEONCHEON, South Korea -- North Korea released water from a border dam without giving prior notice to South Korea on Monday, causing the water levels of a cross-border river downstream to rise dangerously, officials said.

The North opened the floodgates of Hwanggang Dam on the western inter-Korean border, sending water into the Imjin River flowing to the South and causing water levels under the river's northernmost Pilseung Bridge to rise to 5.97 meters as of 5 p.m.

(Yonhap)
It's considered a crisis if water levels under the bridge reach 7.5 meters.

The South's military detected the release on its own as the North gave no prior notice, officials said.

Officials said they're closely monitoring the changes in water levels.

The North's release of dam water can be deadly for those living in low-lying areas along the border river in the South. In 2009, six South Koreans were killed after the North's sudden release of water from the dam.

After the deaths, the North promised to give the South notice before opening the floodgates, but the regime has not done so since its last notification in July 2013. (Yonhap)