The rapid rise in water levels along the Imjin river on 6 September occurred after the North abruptly released a massive amount of water from an upriver dam.
No advance warning was given of the release, which sent a surge of water across the heavily-fortified border between the two Koreas.
Shortly afterwards North Korea said it "urgently" had to open sluice gates because levels behind a dam on the river had become dangerously high.
The release caused the water levels in the river to almost double in a matter of minutes, sweeping to their deaths six South Koreans who were camping downstream and casting a cloud over recent improvements in inter-Korean relations.
North and South Korea remain technically at war, never having signed a peace treaty formally ending the 1950-53 Korean War.
The two sides last held formal talks in August, during which they agreed to resume a stalled programme of family reunions.