Clackamas fire crews are battling a fire at the Blue Heron Papermill in Oregon City early Thursday morning, authorities said.

A fire early Thursday at the site of the former Blue Heron paper mill is expected to smolder for the next 24 to 48 hours, possibly sending smoke and ash over Oregon City, officials said. Regulators with the Oregon Department of Environmental Quality said the fire did not pose a risk to river and air quality.