Wellington City Council says it is becoming increasingly frustrated with a phantom dumper that has been illegally discharging organic material into the wastewater network at Karori since February.
The dumper struck again on Monday morning, blocking intake screens at the city's Western Wastewater treatment plant and preventing regular sewage flow.
The company that operates the wastewater network, Capacity, says operators were able to divert the flow into a storage tank while they cleared the screens of rags and other material.
The tank was 91% full when normal flow was repaired, narrowly avoiding the need to discharge into Cook Strait.
Capacity says the dumpings happen in the early hours of the morning every four to eight weeks, and is appealing for any information that could help identify the source.