North Korea had declared that it would do soon to prevent flooding due to torrential rains.
The water level began to rise up to 10 centimeters every 10 minutes, at Hoengsan, south of the inter-Korean border. South Korea speculated that the move was a part of their attack though the North claimed that it had to do so as its own dam were dangerously high. North Korea also warned Seoul of similar moves in the future.
North has taken the new step in the background of persistent tension in the wake of the March sinking of South Korean warship, Cheonan which is blamed on Pyongyang. The sinking claimed the lives of 46 South Korean sailors. North declared that they are responsible for the sinking and also warned any punishment would trigger war.