Wellington City Council is using cameras inside pipes in the Owhiro Bay beach area to try to locate the source of a sewage leak.
Traces of enterococci, which indicates pollution including sewage, have been recorded at the beach at levels likely to cause health problems.
The beach is closed to the public indefinitely.
Infrastructure planning manager Maria Archer says repairs were made to some sewage pipes on Wednesday, but the council is still baffled about where the contamination is coming from.
Wellington City Council says the public should avoid the water.
Health problems associated with the contamination include diarrhoea, stomach cramps, vomiting and cuts becoming infected.