The Yellowstone River has been contaminated by a train derailment, triggering water conservation warnings downstream.

On Saturday, a bridge over the Yellowstone River collapsed under a train carrying hot asphalt and molten sulfur. Witnesses could see yellow fluid, definitely the sulfur, leaking into the water immediately following the accident. No one was injured in the accident, which derailed ten cars, including seven directly into the river. It is being investigated whether the derailment or the bridge collapse happened first.

Officials immediately shut down downstream drinking water intakes as a precaution. When sulfur mixes with water, it can create sulfuric acid, which obviously would be terrible for both the river and anyone drinking the water. But the size of the river means that it would be extremely diluted, minimizing any long-term impact. The larger threat is the asphalt, which was hot and liquid at the time of the accident, its tar components spreading a thin oil slick downstream. Hardened pieces of asphalt began appearing on riverbanks downstream the following day. Yellowstone and Stillwater County residents aare being asked to conserve water until further notice.

On Sunday, the Montana Department of Environmental Quality tested the water along waterways and treatment facilities in the region and “found no negative impacts,” said David Stamey, the chief of emergency services in Stillwater County. They are not considering the matter a crisis at this time, as the volume and cold temperature of the water are both mitigating any hazards.

Montana Rail Link, the company operating the train, is coordinating cleanup efforts with Montana state officials.

Andy Garland, a Montana Rail Link spokesman, said no one was injured. Mr. Garland said that two other cars were carrying sodium hydrosulfide but neither landed in the water or been breached.

Garland also said Montana Rail Link is “committed to addressing any potential impacts to the area as a result of this incident and working to understand the reasons behind the accident.”

According to the Federal Railroad Administration, there are over a thousand trail derailments each year in the US, between 3-4 each day.