Four fire engines and 21 firefighters and officers were called to a fire in the gym in a block of flats in Western Gateway, Canning Town.
The fire was confined to the sauna in the female changing room. A small amount of the gym was damaged by fire.
The Brigade was called at 1009 and the fire was under control at 1047. Fire crews from Poplar, Plaistow, Millwall, and East Ham fire stations attended the scene.
The fire is believed to have been caused by an electrical fault.