A brush fire at the Mast Landing Audubon Sanctuary in Freeport on Tuesday afternoon may have been caused by an improperly disposed cigarette butt.

A small portion, about 1.5 acres of the 145-acre preserve, suffered fire damage, but no individuals or properties were harmed. The forest canopy remains intact.

Maine Audubon which owns and maintains the preserve along the Harraseeket River estuary, posted a thank you on its website Wednesday to the Freeport Fire Department and neighboring towns that responded to the fire.

The Mast Landing Audubon Sanctuary was closed to visitors Wednesday, but will reopen on Thursday for public use. Anyone who visits the preserve is being asked to be cautious because some hot spots remain. Users are also being asked to report any signs of smoking or smoldering remains to the Freeport Fire Department or to Maine Audubon (207-781-2330).

“While no cause can officially be determined, it is suspected that an improperly disposed of cigarette butt might have been responsible. During the dry season, even the smallest ember can smolder in the duff for days until the relative humidity and winds create the perfect environment for ignition,” Maine Audubon said. “In order to minimize the risk of fire on our sanctuaries, Maine Audubon prohibits the use of smoking products, fire, and open flames of any kind.”

The sanctuary features more than three miles of hiking trails that wind along a stream and tidal marsh and through an orchard, fields, and forest. The preserve is located off Upper Mast Landing Road in Freeport.