Broken pipes and faecal contamination are continuing to plague the Wellington region, most recently in Porirua's Titahi Bay.
Sampling from 19 May in a culvert at the bay's south entrance found the measure of E coli was 300 times the level considered safe to swim.
Wellington Water spokesman Alex van Paassen said this was because of two faults with private connections where sewage pipes were flowing into the stormwater network.
He said one involved a 9m-long collapsed section of a pipe that would take some time to fix.
In a notice sent to the mayor last week, Wellington Water advised that signs warning people not to swim should remain at the bay "as there is a risk that an incoming tide could bring the culvert contamination back onto the beach".
Porirua mayor Anita Baker said the bay would remain closed for swimming until contamination levels came down.
She said she had seen people paddle boarding and body boarding in the bay and warned them to stay out.
"We need to keep it shut until they fix those pipes. From my point of view I do not want anyone swimming in there while there is E coli because that is dangerous.
"We need to be fixing them as fast as we can, but as in Wellington, it's having the capacity to actually do it."
Last week, heavy rain meant 246,000 litres of partly-treated wastewater was released into the Porirua Harbour.
This was a legal discharge and less than a quarter of the volume that would trigger extra sampling.
Baker said she still wanted to know about these discharges, and felt the public should too.
"When we do those discharges, we should tell people. Yes you can do it, but say 'we've just done it' because otherwise people think we have a leak [in the treatment plant]."
In its notice to the mayor, Wellington Water also admitted contractors had mistakenly removed the beach warning signs on 26 May.
The signs were there because of the high readings on 19 May, not because of the legal wastewater discharge and should have remained on display, the notice said.
"The error was corrected the next morning and the signs reinstated. We apologise for any confusion caused," the notice read.
Baker said this is not acceptable.
"So you had the treatment plant people not speaking to the people doing the other leaks and that's where the signs got changed. Those sort of things I don't want happening."