As a result, Dougherty estimated about “60-70% of the plant was inundated” with wastewater, including control and electrical equipment.

“So we’re in a bad way at the moment.”

When asked how bad the failure was on a scale of 1 to 100, Dougherty gave it a 90.

“I can imagine there’s something worse, but I just can’t quite think of it at the moment.”

Dougherty suspected the plant’s outfall, which is about 1.8km long and discharges into the Cook Strait, had been partially blocked.

However, he wouldn’t speculate on what the blockage could be, citing the need to get a camera into the plant to investigate.

“I have some suspicions, but I don’t really want to talk about those in front of all of New Zealand … we’ll want to get to it and find it first,” he said.

“I’m wondering whether we might have some pipe damage, for example … it won’t be wet wipes. That type of thing wouldn’t have caused a blockage as bad as this. And what’s more, they would be unlikely to get past our treatment system into the outfall pipe at any rate.”

Dougherty said the outfall is inspected annually by divers, given the diffuser at the end is most vulnerable to being obstructed, “but it’s very hard to get into a pipe that’s carrying high volumes of wastewater every day and is your only pipe … So I don’t think we have … any regular inspections of that pipe.”

The remedial work had already been a “challenge” for Wellington Water contractors who have worked on the plant as it continued to operate.

“It’s like trying to fly a plane and rebuild it at the same time.”

He wouldn’t say whether the leak breached resource consent, arguing that was for the regional council to decide, but confirmed it is outside what they are allowed to do.

Dougherty found out about the problem at the plant about 7am when he woke up and saw a text alert.

Asked whether his staff should have called to let him know there’d been a catastrophic failure, Dougherty said it was too early to tell.

“I think at that stage, we were still trying to establish the damage. I don’t know that my knowledge any earlier would have made a difference to what is going to be a long, ongoing situation.”

Bridge asked whether the plant failure affected all Wellingtonians, to which Dougherty replied: “I’m afraid so, yes.”

“Some [wastewater] goes to another plant, but the majority of Wellington, yes.”

Wellington Mayor Andrew Little also said an alert about the failure went out to Fire and Emergency at 1am yesterday, instead of going to the contractors responsible for maintenance.

“Wellington Water are telling me they don’t quite understand,” Little said on Ryan Bridge TODAY.

“They were eventually told when Fenz turned up and realised it wasn’t a problem for them. So we need to understand what happened with the alert system, it didn’t seem to function as intended.”

The raw sewage is coming out of a short outfall pipe about 5m off the coast, rather than the long outfall pipe which pumps usually-treated sewage about 2km out to sea.

“This is a big deal,” said Little, noting there were 70 million litres of sewage flowing into the beaches each day, and that it would likely take a few days to redirect it to the long outfall pipe.

“It beggars belief in this day and age that there could be such a catastrophic failure,” he said.

“It’s been there for 30 years, it’s had all the upgrades and maintenance expected. There’s been nothing indicated to me that the plant’s at risk or in need of replacement.”

Wellington City Council has warned people to stay away from beaches on the South Coast, including Owhiro Bay to the west and around to Breaker Bay. Wellington Water will be monitoring water quality around to Seatoun.

“For the sake of your own health, stay away,” Little said.

Little himself was told about the failure about 6.30am on Wednesday, but said it was another couple of hours before he was “advised about the gravity of the problem … that it was a complete plant failure”.

It could take months to repair the damaged equipment, Wellington Water said yesterday.

The site was evacuated after multiple floors were inundated with untreated wastewater.

Speaking to media yesterday, Dougherty said the cause of the issue was not yet known, with electrical equipment in the plant submerged in sewage and some areas still inaccessible.

He described the facility as like a house under water.

“Our immediate focus is restoring power to the plant, resuming service, and diverting wastewater,” Dougherty said in an earlier statement.

“Wellington Water has set up an emergency management team and [is] working at pace to stabilise the situation.”

The facility, near the city’s airport, is expected to be closed for “an extended period”, the organisation said.

Dougherty said Wellingtonians should not be concerned about using their amenities as usual, saying things like flushing a toilet would not be an issue.

A Herald photojournalist at the scene yesterday said a strong sewage odour could be smelled at the beach near the facility, and toilet paper and murky sewage water could be seen in the sea.

‘I will be asking hard questions’ – Local MP

Rongotai MP Julie Anne Genter said the news of the incident is a “terrible reminder of the importance of investing in our infrastructure and ensuring that we are working with nature to protect our wai and our moana”.

“This will be hugely disappointing for all those Wellingtonians who love to swim, surf, snorkel, gather kai and make the most of our beautiful coast,” Genter said.

“Clearly this is unacceptable and, once the initial problem is fixed, I will be asking hard questions about just how this happened and what we need to do to stop it from happening again.”