The state fire marshal's office says an electrical problem caused last month's fire at the historic Bluenose Inn overlooking Bar Harbor.
The investigation also revealed that the inn's sprinkler system had been shut off. It took 21 hours to put the fire out. Crews from several towns in Hancock and Penobscot counties joined the Bar Harbor Fire Department in responding to the fire.
No employees or firefighters were hurt, the state said.
The fire started in the annex of the hotel, and the state estimates it caused $10 million in damage.
In an update on the hotel's Facebook page, Bluenose managers said the main building was unharmed, and they plan to operate it as usual for the upcoming summer season.
