The restaurant, a two story wood framed building, is located at 875 North Shore Drive, at the end of a long dock.
Authorities say the origin of the fire occurred in the upstairs wall on the south side of the structure where the fryers are used.
Investigators listed the cause as "radiant heating of the wall (exothermic decomposition), continuing over a long period of time, in a confined space, which led to slow oxidation of a combustible material. At this point, spontaneous ignition took place."
The fire’s unique circumstances did not release enough heat to activate the pier’s fire alarm or suppression system.
Interviews, plus a thorough examination of the evidence led to the fire origin and cause determination, a report said. There was nothing found to indicate any malicious intent or negligence in connection with the fire, according to the report.