Rapid warming in the region led to an influx of water in the river basin and when a wall of ice got hung up in a curve in the river, it caused that water to back up and flood Galena, said Kerry Seifert, operations section chief at the Alaska Division of Homeland Security and Emergency Management.
"We expect the flooding to become worse before the waters start to recede," Alaska Gov. Sean Parnell said.
Some 300 people who live in Galena were evacuated to Fairbanks and Ruby, where some are staying with friends and family, and others are at shelters, CNN reported Thursday.
"Ensuring the safety of those impacted by the flooding remains my top priority," Parnell said.
Water appeared to be moving around the ice jam Wednesday, Seifert said. When the ice jam breaks, there could be a flooding risk downriver in Koyukuk and Nulato.