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Last updated: 19 February 2026

The latest on the stench

As you know, over the past month or so, we’ve experienced significant challenges with the Christchurch Wastewater Treatment Plant's oxidation ponds – unexpectedly, conditions were the worst they've been since the fire.

Usually at this time of year, the ponds are healthy, but several compounding factors have contributed to the stench.

The latest on pond health and odour 

We know that the odour was particularly noticeable for a period this morning (19 February), and this was picked up on some of odour monitors. We’re sorry for the disruption this may have caused.

While we had taken steps to manage the impact of the recent rainfall event, these situations are unpredictable and we knew some odour was possible. Weather conditions have since improved, and the odour has largely subsided.

Odour levels can change quickly, particularly with shifts in weather and other environmental factors. We are continuing to closely monitor the situation and will keep the community updated as soon as we can if there are any further changes.

We’ll keep doing everything we can to track these changes and update you as early as possible.

The recent storm and then more settled weather conditions over the last 36 hours have seen an increase in odour from the ponds for a period this morning and a change in our odour assessment, with a higher probability of odour from some of the ponds.

Although Pond 2A has high algae concentration, the results of dissolved oxygen were low and there is low algae concentration in Pond 5 and 6.

Staff are monitoring the odour and making changes where possible. We’re continuing hydrogen peroxide dosing and all of our aerators are operating.

We're developing a pond management plan 

A pond management specialist has been on site with our team to help develop a new, comprehensive pond management plan. This plan will focus on tracking key indicators – such as algae levels, dissolved oxygen, and other early‑warning signs – as well as making some recommendations so we can act sooner when conditions begin to deteriorate.

The aim is simple – reduce the chance of odour by identifying issues earlier, responding faster, and keeping the community better informed.

We want to reassure you that we’ve already been extensively monitoring these key pond indicators. The new pond management plan builds on this work by strengthening our approach – setting clearer trigger points for when conditions start to shift and outlining earlier, more decisive actions we can take.

Improving access to hydrogen sulphide information

We know the community is eager to have clearer, more up‑to‑date information about hydrogen sulphide (H₂S) levels, and we want to reassure you that this work is a priority for us. Our team is committed to improving transparency and making it easier for residents to understand what’s happening in their area.

We already have strategically placed hydrogen sulphide monitors around the oxidation ponds and nearby neighbourhoods to track levels, and we’ve doubled our odour assessment frequency, with updates now posted twice a week on our website.

Behind the scenes, we’re working on the next stage – making indicative additional hydrogen sulphide data available directly on our website. Once the dashboard is ready, residents will be able to view more recent readings at a glance.

There’s still some technical and testing work to get through before we can launch this, and while we don’t yet have a confirmed launch date, we want you to know that this is well underway. We’re pushing it forward as quickly as we can and we’ll continue to keep the community updated as the work progresses.

Neighbourhood visits

Thank you to all the residents we spoke with on our neighbourhood visits. The kindness, openness, and understanding we received at your doors meant a great deal to our team. We know the stench has been challenging, and we truly appreciate the time people took to talk with us.

Our team visited 750 homes and received 545 responses. For those who weren’t home, we left a calling card with our contact details. If you’d like to speak with us, please give us a ring and leave your name and phone number – we’ll happily arrange a time to call you back.

A clear message came through in our conversations: you want this issue resolved as quickly as possible, and we hear you. These visits were an important step in listening directly to the community, and we’re committed to doing more of this – spending real time with people, answering questions, and hearing concerns firsthand. We expect to be able to share more later this week about the next steps.

Council staff member Gary Watson is working alongside the local Councillors and Community Board to support good information flow and to look at ways to help make living in the area as positive as it can be while the plant is rebuilt.

Gary will be based in the community to be as accessible as possible. We're yet to confirm a base for Gary, but in the meantime he will be at the Bromley fair on Saturday 21 February cooking the barbeque if you are interested in a chat or you can email him at gary.watson@ccc.govt.nz.

Long-term solution

Once commissioned, the new activated sludge reactor will address the long‑standing odour issues that followed the fire. We are actively looking for opportunities to accelerate this programme wherever possible, though the timeline is already extremely tight. We’ll continue to make the most of any chance to bring that work forward.

Work on site is progressing well, and excavation is now in full swing. Crews are steadily removing soil from the site, with the average depth reaching about two metres below ground. This will create the platform needed for installing the stone columns later on.

Next week, the team will move closer to the plant to carry out some exploratory work. This includes locating any existing services that may still be in the ground from the old trickling filter and removing what’s no longer needed. Doing this will allow us to install sheet piling and safely excavate along the temporary bypass line that was put in after the fire.

For the next few weeks, the focus will be much the same – dig, dig, and more digging – as we continue preparing the site for the next stages of construction.

The overall programme is expected to span about three years, with commissioning targeted for 2028. Importantly, we’re able to build the new activated sludge reactor with minimal disruption to current operations.

What caused the stench

Each year, the wastewater load which arrives over the holiday period varies significantly as industry shuts down for the summer holiday and our population varies. The temporary activated sludge plant, which is a biological process, doesn't manage this variation very well.

This can result in the temporary plant struggling and passing additional load to the ponds, however, usually at this time of year the ponds are very healthy and are able to pick up the slack.

On top of this, we expected the high levels of rain in January to help flush wastewater through the system and improve pond health; however, this didn't happen, as it appears to have set back the algae growth in the ponds.  

While we know the weather and high load are contributing factors, our team is reviewing all data to understand whether other factors also played a role in the current situation.

We’ve always known we're operating the temporary plant with a narrow margin for error, as it has no extra capacity. This makes the system more vulnerable to sudden changes. While the ponds are now showing signs of improvement, much of the recovery depends on natural processes such as algae growth and oxygenation.

Health, wellbeing and support services

We’re sorry for the impact this continues to have on you and your whānau. Please be assured we are doing everything we can to support the system’s recovery and reduce odour where possible.

Here's the latest advice from Dr Imogen Evans, Public Health Medical Specialist for the National Public Health Service:

"Exposure to hydrogen sulphide stench arising from the Christchurch Wastewater Treatment Plant can cause nausea, headaches, eye and throat irritation, skin irritation, sleep disturbance, and worsening asthma symptoms at relatively low concentrations. 

"If people exposed to the stench don't experience physical health effects, continued exposure to unpleasant or nasty, noxious stench can still have an adverse effect on people's mental wellbeing. 

"While exposure to hydrogen sulphide is unpleasant and may result in health effects, it doesn’t accumulate in the body. Any health effects would be expected to resolve when the odours are brought back to normal levels, and long-term health effects are highly unlikely.

"People experiencing health issues as a result of the stench coming from the treatment plant should seek health advice from their GP, doctor, Hauora or healthcare provider, or call Healthline free on 0800 611 116, anytime 24/7 for advice as soon as possible. In an emergency call 111."

There are also free services across Ōtautahi Christchurch available to support and enhance overall health and wellbeing. These include:

Health Improvement Practitioners (HIPs)

HIPs are qualified mental health professionals based in General Practices (GPs). They offer free, 15 to 30-minute sessions focused on practical strategies to support mental and physical wellbeing. There is no limit to the number of sessions you can access. You can book directly through your GP.

Pae Ora ki Waitaha Support

Pae Ora ki Waitaha is a free healthy lifestyles service developed with Māori and Pasifika providers.

More information is available on their website(external link).

Healthline

Healthline is a free over-the-phone health service available 24 hours a day, seven days a week. If you or someone in your family is unwell, you can call Healthline and speak to experienced nurses and paramedics for health advice and information about what to do next.

Call 0800 611 116.

Timeline of key events and decisions

November 2021

  • On 1 November 2021, emergency services respond to a fire at the Wastewater Treatment Plant in Bromley. Both of the trickling roof filters collapse. The damage couldn't be assessed properly until the fire was completely out.
  • On 4 November, the Council installed a sprinkler system to remove hot spots and help reduce the smell. We also begin working on an adaptive management plan to figure out the best possible outcome for the discharge of wastewater from the plant.
  • On 26 November, the fire is officially completely extinguished by the fire service. The Council identifies the need to remove the two trickling filters. Both filters store 13,000 cubic metres of material.
  • The Council started using misters and polyaluminium chloride - an odourless powder that dissolves in water - to help suppress the smell. Polydosing also settles more of the suspended solids in the wastewater, improving the water quality as it progresses through the plants.
  • Hydrogen peroxide - a compound that naturally breaks down into water and oxygen – starts to be added to the wastewater before it’s discharged into the oxidation ponds.

December 2021

  • On 6 December, the Council completed a successful trial to remove a section of the fire-damaged media from the plant. This means the Council could begin assessing the stability of the structures.
  • On 17 December, Council staff planned to convert two of the plant’s four clarifier tanks (or secondary contact) into aeration tanks. Installing four aerators in each of the two tanks will help decrease the bad smells and improve the quality of the wastewater being discharged. The Council anticipated that it would be years before the trickling filters could be replaced or rebuilt.

February 2022

  • On 14 February, aeration components begin to arrive to implement the interim plan to minimise odours from the fire-damaged plant.

March 2022

  • On 16 March, eight aerators are installed in two of the plant’s four clarifiers.
  • Soon afterwards, increased odours from the trickling filters are detected after wet weather. It's determined that the acute stench is caused by the material inside the trickling filters rotting and drying out.

April 2022

  • On 6 April, the aerators installed in March are turned on.
  • On 12 April, the Council decided to fast-track the appointment of a contractor to remove the burnt filter material.

May 2022

  • Filter media removal work starts.
  • On 6 May, independent testing to better understand the odours from around the fire-damaged plant detects small amounts of hydrogen sulphide and methyl mercaptan.
  • On 26 May, the Council confirms a community support package for 3,380 of the most affected residents.

June 2022

  • Southern Demolition and Salvage Limited conducted a test run, removing and transporting the burnt trickling filter material on Friday 3 and Saturday 4 June.
  • Work to remove the trickling filter began on 6 June.

July 2022

  • The new activated sludge treatment process becomes fully operational at the plant.
  • This new system pumps wastewater from the converted aeration basins to the clarifiers, which greatly improves the quality of the wastewater.

August 2022

  • Trickling filters are emptied one month ahead of schedule.

September 2022

  • Odours from the oxidation ponds are expected to reduce from September, although it is expected that some odours will remain for most of the month. These will progressively reduce as the pond's health improves.

April 2023

  • A project to increase the biological health of Pond 1 is completed after 16 aerators are installed and turned on, churning more than 300kg of oxygen into the pond every hour.
  • In the long term, these aerators will ensure the entire pond continues to stay healthy and function well.

May 2023

  • The disc aerators on Pond 1 failed and were in the process of getting repaired.

Late 2023

  • Fencing around oxidation ponds was installed to improve safety and reduce rubbish entering ponds. Subsequent minor changes were made to deter birds and improve effectiveness.
  • Insurance negotiations were continuing.
  • In November, a report on the insurance claim for the November 2021 fire was provided to the Council. 
  • In December, aerators on Oxidation Pond 1 restarted to minimise odours.

March 2024

  • A report on the insurance process and odour mitigation efforts was provided to the Council.
  • Odour mitigation plan released. 
  • Odour mitigation work is underway. Various actions taken to improve plant performance and reduce odour. 
  • A new interactive map was created showing odour mitigation work. 

April 2024

  • Ponds switched to winter operation mode. Adjustments made to our operations to reduce odours when the biology changes as weather cools. 

May 2024

  • The Mayor and councillors approved a grant of $130,000 to resource a project with the goal of strengthening and sustaining effective and respectful relationships with Eastern Communities.
  • Completed work to cover inlet chambers to contain odour. 
  • Completed replacement of the bio-bed material in the odour control system. Old material reused as soil conditioner for native planting areas.

October 2024

  • Christchurch City Council and its insurers have agreed on a settlement in relation to the fire-damaged trickling filters at the Christchurch Wastewater Treatment Plant.
  • The Council also approved the replacement of the trickling filters with an activated sludge reactor.
  • This significant milestone allows us to move forward with building a resilient and more environmentally friendly wastewater treatment plant for our growing city.
  • Replacing the trickling filters with an activated sludge reactor will give the Council the opportunity to significantly reduce greenhouse gas emissions. Additionally, activated sludge reactors can deliver better environmental outcomes and have a smaller footprint that can be cost-effectively upsized to accommodate the needs of our growing population.
  • Design work is underway and it’s expected to take up to three years to complete the design and construction of the new activated sludge reactors.

November 2024

  • Demolition of the Christchurch Wastewater Treatment Plant’s fire-damaged trickling filters started.
  • Southern Demolition is doing the work, which is expected to take four to five months to complete. 
  • The demolition is the first stage of physical work to replace the filters with an activated sludge reactor, which will fix long-standing odour issues. 

April 2025

  • Demolition of the trickling filters was completed making way for construction to begin on the the new activated sludge reactor later this year. 

February 2026

  • The bulk earthwork started. This will be completed in four stages and is expected to finish around early April 2026 .  

April 2026

  • The installation of approximately 1400 stone columns will begin. This will take approximately four months to complete.
  • Installation of the reactor discharge pipe and the Returned Activated Sludge (RAS) line to commence. This is expected to be completed in late October.

June 2026

  • Work to install an engineered gravel platform will begin.  

August 2026

  • The engineered gravel platform work is expected to be completed.
  • Construction of the concrete structure for the new reactor will begin. This is a major part of the project and will take around one year to complete.

October 2026

  • Installation of the reactor discharge pipe and the Returned Activated Sludge (RAS) line expected to be completed.
  • The process to install the supply pipes from the existing pump station to the new plant will begin. Due to the pipes’ depth, sheet piling will be required for all underground pipes. This will be completed around March 2027.

2027

  • Construction of the blower hall will commence. This will house the blowers and electrical room. It will be constructed with precast concrete panels. This will take around four months to complete.
  • The installation of the supply pipes from the existing pump station to the new plant will finish up around March.
  • The blower hall is expected to be completed around April.
  • Installation of all the equipment and pipes required to operate the new plant will commence. This will start with the blower hall fit-out and then move on to the reactor.
  • Pumps and pipework in the existing pump station will be replaced to accommodate the new plant.
  • Construction of the concrete structure for the new reactor is expected to be completed around August 2027.

2028

  • Commissioning the new plant and replacing the remaining two pumps in the pump station will begin. This will enable us to shut down the existing temporary activated sludge plant and prepare to return the two clarifiers to their original purpose.
  • Removing the temporary plant and making any repairs to the clarifiers and other equipment to return them to normal duty.
  • The entire project is expected to be completed in late 2028.

November 2021

  • On 1 November 2021, emergency services respond to a fire at the Wastewater Treatment Plant in Bromley. Both of the trickling roof filters collapse. The damage couldn't be assessed properly until the fire was completely out.
  • On 4 November, the Council installed a sprinkler system to remove hot spots and help reduce the smell. We also begin working on an adaptive management plan to figure out the best possible outcome for the discharge of wastewater from the plant.
  • On 26 November, the fire is officially completely extinguished by the fire service. The Council identifies the need to remove the two trickling filters. Both filters store 13,000 cubic metres of material.
  • The Council started using misters and polyaluminium chloride - an odourless powder that dissolves in water - to help suppress the smell. Polydosing also settles more of the suspended solids in the wastewater, improving the water quality as it progresses through the plants.
  • Hydrogen peroxide - a compound that naturally breaks down into water and oxygen – starts to be added to the wastewater before it’s discharged into the oxidation ponds.

December 2021

  • On 6 December, the Council completed a successful trial to remove a section of the fire-damaged media from the plant. This means the Council could begin assessing the stability of the structures.
  • On 17 December, Council staff planned to convert two of the plant’s four clarifier tanks (or secondary contact) into aeration tanks. Installing four aerators in each of the two tanks will help decrease the bad smells and improve the quality of the wastewater being discharged. The Council anticipated that it would be years before the trickling filters could be replaced or rebuilt.

February 2022

  • On 14 February, aeration components begin to arrive to implement the interim plan to minimise odours from the fire-damaged plant.

March 2022

  • On 16 March, eight aerators are installed in two of the plant’s four clarifiers.
  • Soon afterwards, increased odours from the trickling filters are detected after wet weather. It's determined that the acute stench is caused by the material inside the trickling filters rotting and drying out.

April 2022

  • On 6 April, the aerators installed in March are turned on.
  • On 12 April, the Council decided to fast-track the appointment of a contractor to remove the burnt filter material.

May 2022

  • Filter media removal work starts.
  • On 6 May, independent testing to better understand the odours from around the fire-damaged plant detects small amounts of hydrogen sulphide and methyl mercaptan.
  • On 26 May, the Council confirms a community support package for 3,380 of the most affected residents.

June 2022

  • Southern Demolition and Salvage Limited conducted a test run, removing and transporting the burnt trickling filter material on Friday 3 and Saturday 4 June.
  • Work to remove the trickling filter began on 6 June.

July 2022

  • The new activated sludge treatment process becomes fully operational at the plant.
  • This new system pumps wastewater from the converted aeration basins to the clarifiers, which greatly improves the quality of the wastewater.

August 2022

  • Trickling filters are emptied one month ahead of schedule.

September 2022

  • Odours from the oxidation ponds are expected to reduce from September, although it is expected that some odours will remain for most of the month. These will progressively reduce as the pond's health improves.

April 2023

  • A project to increase the biological health of Pond 1 is completed after 16 aerators are installed and turned on, churning more than 300kg of oxygen into the pond every hour.
  • In the long term, these aerators will ensure the entire pond continues to stay healthy and function well.

May 2023

  • The disc aerators on Pond 1 failed and were in the process of getting repaired.

Late 2023

  • Fencing around oxidation ponds was installed to improve safety and reduce rubbish entering ponds. Subsequent minor changes were made to deter birds and improve effectiveness.
  • Insurance negotiations were continuing.
  • In November, a report on the insurance claim for the November 2021 fire was provided to the Council. 
  • In December, aerators on Oxidation Pond 1 restarted to minimise odours.

March 2024

  • A report on the insurance process and odour mitigation efforts was provided to the Council.
  • Odour mitigation plan released. 
  • Odour mitigation work is underway. Various actions taken to improve plant performance and reduce odour. 
  • A new interactive map was created showing odour mitigation work. 

April 2024

  • Ponds switched to winter operation mode. Adjustments made to our operations to reduce odours when the biology changes as weather cools. 

May 2024

  • The Mayor and councillors approved a grant of $130,000 to resource a project with the goal of strengthening and sustaining effective and respectful relationships with Eastern Communities.
  • Completed work to cover inlet chambers to contain odour. 
  • Completed replacement of the bio-bed material in the odour control system. Old material reused as soil conditioner for native planting areas.

October 2024

  • Christchurch City Council and its insurers have agreed on a settlement in relation to the fire-damaged trickling filters at the Christchurch Wastewater Treatment Plant.
  • The Council also approved the replacement of the trickling filters with an activated sludge reactor.
  • This significant milestone allows us to move forward with building a resilient and more environmentally friendly wastewater treatment plant for our growing city.
  • Replacing the trickling filters with an activated sludge reactor will give the Council the opportunity to significantly reduce greenhouse gas emissions. Additionally, activated sludge reactors can deliver better environmental outcomes and have a smaller footprint that can be cost-effectively upsized to accommodate the needs of our growing population.
  • Design work is underway and it’s expected to take up to three years to complete the design and construction of the new activated sludge reactors.

November 2024

  • Demolition of the Christchurch Wastewater Treatment Plant’s fire-damaged trickling filters started.
  • Southern Demolition is doing the work, which is expected to take four to five months to complete. 
  • The demolition is the first stage of physical work to replace the filters with an activated sludge reactor, which will fix long-standing odour issues. 

April 2025

  • Demolition of the trickling filters was completed making way for construction to begin on the the new activated sludge reactor later this year. 

February 2026

  • The bulk earthwork started. This will be completed in four stages and is expected to finish around early April 2026 .  

April 2026

  • The installation of approximately 1400 stone columns will begin. This will take approximately four months to complete.
  • Installation of the reactor discharge pipe and the Returned Activated Sludge (RAS) line to commence. This is expected to be completed in late October.

June 2026

  • Work to install an engineered gravel platform will begin.  

August 2026

  • The engineered gravel platform work is expected to be completed.
  • Construction of the concrete structure for the new reactor will begin. This is a major part of the project and will take around one year to complete.

October 2026

  • Installation of the reactor discharge pipe and the Returned Activated Sludge (RAS) line expected to be completed.
  • The process to install the supply pipes from the existing pump station to the new plant will begin. Due to the pipes’ depth, sheet piling will be required for all underground pipes. This will be completed around March 2027.

2027

  • Construction of the blower hall will commence. This will house the blowers and electrical room. It will be constructed with precast concrete panels. This will take around four months to complete.
  • The installation of the supply pipes from the existing pump station to the new plant will finish up around March.
  • The blower hall is expected to be completed around April.
  • Installation of all the equipment and pipes required to operate the new plant will commence. This will start with the blower hall fit-out and then move on to the reactor.
  • Pumps and pipework in the existing pump station will be replaced to accommodate the new plant.
  • Construction of the concrete structure for the new reactor is expected to be completed around August 2027.

2028

  • Commissioning the new plant and replacing the remaining two pumps in the pump station will begin. This will enable us to shut down the existing temporary activated sludge plant and prepare to return the two clarifiers to their original purpose.
  • Removing the temporary plant and making any repairs to the clarifiers and other equipment to return them to normal duty.
  • The entire project is expected to be completed in late 2028.