The Stillwater County Disaster and Emergency Services said on Facebook​ that "multiple" rail cars were in the river, but the cause of the derailment had not yet been determined.

The Yellowstone County Sheriff’s Office wrote on Facebook on Saturday morning that multiple tanker cars were “damaged and leaking petroleum products near the Yellowstone River.”

Later reports from other agencies in addition to photos from the derailment indicate that the train had crashed into the Yellowstone River when a bridge collapsed early Saturday morning.