A relay failure in the Marathon sewer system Friday night into Saturday led to sewage bubbling to the surface.
City Planning Director George Garrett said it was confined to the treatment plant at the east end of Florida Keys Marathon Airport but some people reported sewage flowing from toilets and other sources in the city's Little Venice area.
Those reports indicated it started in the evening Friday. Garrett said it was under control early Saturday.
In other utility issues, widespread Comcast Cable outages were reported behind the airport overnight Friday into Saturday.