Continuous rain fell throughout September 19, resulting in widespread mudslides that killed over 2,000 people. A large mudslide blocked the Choloma River, preventing water from the river and the accumulated of rain caused by Fifi from reaching the ocean. The waters were released from this natural dam on September 20, when a concrete bridge broke upstream and tore through the mudslide. The torrent of water flowed down the valley, triggering a massive flood. The city of Choloma was decimated, with an estimated 2,800–5,000 people killed out of a population of 7,000. This accounted for roughly 20–25% of the storm's total fatalities. The flood occurred during the nighttime, so most residents were unaware of the impending catastrophe.