The fire was reported as an attic fire shortly before 4 p.m. onWagner Road near Simplot Boulevard, just off Idaho 19, Canyon County dispatch reports.
The fire gutted the Water Treatment Office at the Simplot plant, and officials said no one was inside the building. No other buildings around the Simplot plant caught fire.
The fire was originally called in as a two-alarm fire as a precaution, dispatchers said. Caldwell Fire Department is the lead agency, and crews from other agencies, including Star and Wilder, responded. Smoke was visible from Interstate 84.