The Derna dam collapses were the catastrophic failures of two dams in Derna, Libya, on the night of 10–11 September 2023, in the aftermath of Storm Daniel. The collapse of the Abu Mansour Dam and the Derna Dam released an estimated 30 million cubic meters of water, causing flooding downstream as the Wadi Derna overflowed its banks. The floods partially destroyed the city of Derna. The official death and missing persons toll was over 7,800 according to government figures, however, unofficial estimates of the death toll and missing were higher. The event was the second-deadliest dam failure in history, after the 1975 Banqiao Dam failure in China.