The Salt River Pima-Maricopa Fire Department responded early Sunday to the new OdySea Aquarium in Scottsdale to try to locate the cause of smoke inside the building.
Firefighters say the smoke set off an alarm and drew their response.
Crews found smoke and traced it to an air-conditioning unit.
Investigators believe an electrical issue is the cause.
The aquarium's own maintenance crews are working to repair the unit.
The aquarium is open Sunday and will continue normal operations.