The sediment plume, traveling at less than 2 km an hour, now lies about 80 miles upstream from the oil sands production hub of Fort McMurray in northern Alberta.

A spokeswoman from the Alberta Environment and Sustainable Resource Development (AESRD) said downstream communities had been warned not to draw from the river. “We have asked community water treatment plants to refrain from using the river when the plume is going through,” she told Reuters.

Sherritt officials said they have not recorded serious contamination before AESRD delivered an order to implement recovery, management and assessment plans, however. “We began our testing the morning after this happened and the sediment traveling downstream poses no risk to human health or safety,” said Sean McCaughan, Sherritt’s senior vice president for coal.

An AESRD investigation to determine whether Sherritt had violated environmental laws, and whether fines will be issued, is pending, according to authorities.