A three-story barn on Ram Island in the Mystic River was destroyed by fire on Wednesday, and a lamb inside was missing and may have been killed, officials said.

A preliminary investigation shows the fire may have been started by a heating device, fire officials said.

Mystic and Noank fire departments, along with the U.S. Coast Guard, responded to the fire after 3 p.m. Wednesday, according to Mystic Fire Chief Fritz Hilbert.

In addition to the lamb, horses and dogs were inside the barn but survived.

Firefighters were able to douse the fire with the regional fire boat and extended lines from the mainland.

The island has of several structures, including a seasonal home, but no one was there at the time of the fire Hilbert said.

The Stonington Fire Department's Fire Marshal's office is investigating.