Christchurch Mayor Phil Mauger has warned the stench from the city’s wastewater treatment plant could happen again, admitting the system is operating beyond capacity as residents continue to suffer.

Speaking to Chris Lynch Media, Mauger said the council had heard loud and clear that explanations about technology meant little to people living near the oxidation ponds.

“This is about people’s wellbeing,” Mauger said. “It’s all very well for someone in the centre of town to say it smells a bit. These people have had it right up to here for a long time.”

Mauger said councillors were briefed earlier in the day on Wednesday, including a presentation from Coastal Ward councillor Jackie Simon, who made it clear the immediate focus had to be on those most affected.

He said the council was now moving toward a more hands on response, including working with health providers and directly engaging with residents.

“We need to look after the people in the immediate area,” he said.

While work on the new activated sludge system was underway, Mauger said it remained around 3 years from completion, with further work required to connect it to existing infrastructure.

“The system is running at about 105 percent,” he said. “The staff down there deserve a medal for keeping it going, but that doesn’t help the people living with this.”

Mauger said the recent stench was triggered by a surge in waste before Christmas combined with extended gloomy weather, creating low oxygen conditions in the ponds.

To suppress the smell, the council has installed aerators in the first pond, is adding more to the second, and is using jet boats to stir the water and increase oxygen levels.

“If jet boats have to run around those ponds for the next 2 years and that keeps the smell down, then that’s what we’ll do,” he said.

Mauger said the council had already spent about $4 million on aerators and roughly $20 million across the plant on interim upgrades and mitigation measures.

He said chemical dosing, including hydrogen peroxide, should have been introduced earlier and would now be used aggressively if it helped control odour.

“I don’t really care what it costs,” Mauger said. “If it helps, we do it.”

Residents have reported health effects including headaches, vomiting, depression, and impacts on children. Mauger said compensation had not yet been discussed, but support options were now being actively considered.

“Last time we were handing out $200 cards,” he said. “That’s no good to someone with a headache. They want help that actually addresses the problem.”

Mauger said door to door welfare checks were being considered in the worst affected areas to better understand what residents needed.

Bypassing the ponds and sending wastewater directly to sea was technically possible but would require a new pipeline and be extremely costly, making it an unlikely option.

He said there were early signs conditions were improving, with oxygen levels rising and water clarity improving, but warned the risk remained.

“I’m not saying it smells like roses,” Mauger said. “But it is under better control today than it was.”

Mauger said his message to residents was one of honesty.

“There is no doubt it was bloody awful over the last month,” he said. “The reality is it could happen again, and our job now is to do everything we can to stop it and support the people who’ve been living with it.”