An estimated 100 to 1,000 gallons of the water spilled onto the tundra and into Red Dog Creek, which is no longer frozen, the agency said in an initial report. The mine is operated by Teck Alaska.

According to the department, the spill of “process water” occurred at about 2:30 a.m. at the Red Dog Mine, located around 80 miles north of Kotzebue.