Get the latest news and meeting reports on the wastewater treatment plant recovery. We'll be updating this page as required if the situation changes or there is new information.

Latest news and updates

Odour control system upgrade complete

9 May 2024

We've recently replaced the odour control system's bio-bed material. The bio-beds are made out of biological material such as bark and seashells, which are home to millions of microorganisms that break down and filter out odorous gases such as hydrogen sulphide. This material needs to be replaced roughly every 5 to 10 years so it keeps working effectively.

We're also re-using the old material that has broken down over time. Through this process it becomes a highly effective soil conditioner, and we've used it in our native planting areas surrounding the oxidation ponds as part of the midge control programme.

Secondary contact tank inlet chambers covered

The secondary contact tank inlet channels were identified as a source of odour during the on-site monitoring programme. We've recently completed work to cover these inlet chambers as they have the most surface disturbance. This will help contain the odour within the channels and will reduce the dispersal into the atmosphere.

Ponds operating in winter mode

We're now a few weeks into operating the oxidation ponds in winter mode in an effort to reduce odours.

Last year there was an increase in odour when temperatures dropped and the biology of the ponds changed. This hasn't happened yet this year, but with the cooler weather we've been having, we expect it will occur within the next few weeks.

As part of these changes, we're directing wastewater past the oxidation ponds nearest residential properties. This reduces the retention time within the pond system, which should reduce the duration and intensity of any odour event.

We won't know if this approach is successful until the biology of the ponds changes. We're keeping a close eye on the ponds and will be monitoring to see if the changes are effective in reducing odour.

Fencing around oxidation ponds

Late last year a fence was installed around the perimeter of the oxidation ponds to improve safety and prevent unauthorised access to the ponds.

Unfortunately, a couple of issues have arisen as a result of the more secure fence line, including the hemming in of birds between the fence line and the state highway, as well as catching more rubbish on the fence line, which was previously getting through the old fence and into the ponds. We've made some minor changes to the fence line to deter the birds from walking between the fence line and the state highway, which appears to have some success, but we will be closely monitoring this.

This land is owned and maintained by NZ Transport Agency Waka Kotahi. We're working with them on an approach to rubbish collection going forward and will provide more information when we can. 

Funding approved to improve relationship with Eastern Communities

On Wednesday 1 May 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. The project will include:

  • Appointment of an external facilitator to work to understand the needs of the community and to build social cohesion.
  • Appointment of a project manager to facilitate an internal team within Council to assist with understanding the community’s needs, rebuild trust with the community and prioritise what matters most to them.
  • Appointment of a coordinator to assist with the Wastewater Treatment Plant Response in order to improve the reach of the Council to communities that we have not been able to engage with.
  • Prioritise two employees from the Civil Defence Team to focus on coastal response planning, community response planning for the Waitai Board area, tsunami warning, and risk planning.
  • Implement quick wins for the community to show that the Council is hearing and responding to their concerns.

The first step will be to work with the Waitai Coastal-Burwood-Linwood Community Board, as they will be the governance oversight for the project. More information about this project will be made available in future, once the project gets underway.

New interactive map

28 March 2024.

We’ve produced an interactive map(external link) that shows what we’ve got planned or underway to address odour at the Wastewater Treatment Plant. Selecting any of the hot spots on the map will show you a description of what work is being done to address odour at each source.

We’ll keep this map and webpage up-to-date as our work changes.

Odour mitigation work underway

18 March 2024

We recently submitted an odour mitigation plan(external link) to Environment Canterbury in response to issues raised in a Compliance Monitoring Report.

The plan outlines the many actions we’re taking to address odour at the Christchurch Wastewater Treatment Plant to address the issues, improve the performance of the plant and lessen the impact on the community.

We’ve provided an update below on some of the key actions currently underway at parts of the plant. We’ll continue to provide updates on this work and any additional actions that happen in future.

Screen room – a temporary ventilation system has been installed in the screen room and consultants are looking into a permanent system.

Primary settlement tanks – this is where the majority of odour is coming from and we have a range of work underway to improve their performance:

  • We’ve reduced the number of tanks in service to move sewage through the system more quickly. Following an electrical failure we had to return one tank to service. We intend to get back down to four tanks as soon as possible.
  • We’re doing manual daily scum removal.
  • We’ve engaged a contractor to investigate the possibility of a containment system to address odour.
  • We’re investigating covering chambers where there is significant surface disturbance.
  • We’re investigating improving the automatic water spray scum removal system.

Temporary secondary treatment – a consultant is working over 18 weeks to improve this phase of treatment.

Odour control system – we have three bio-bed systems to address odour. We’ve rewired the system to get more fans working and are doing more proactive maintenance. We’re engaging a contractor to renew the remaining bed media.

Oxidation ponds – all aerators are in service and expected to remain so. On 8 March we briefly turned all aerators off to carry out critical maintenance work. This went well and didn’t cause additional odour. There is no further planned maintenance coming up and all aerators are available as we head into winter.

Digesters – investigations revealed the pipework is slightly too small. A project is in the final stages to upsize this. We’re also doing more proactive maintenance.

Odour monitoring – the intensive odour monitoring service is underway and continuing beyond the initial four weeks.

Transition to winter  we’ve developed a plan to minimise the odour from the ponds during the summer to winter transition. This is being checked over the next week and will be put in place by the end of the month.

Website changes – we’re working on making changes to our website so it’s easy to see what odour mitigation work is underway. We expect this to be available in the next week or so.

Odour mitigation plan published

11 March 2024

 An odour mitigation plan for the Wastewater Treatment Plant has been released by Christchurch City Council.

The plan was produced in response to issues raised in a Compliance Monitoring Report from Environment Canterbury, following reports of odour in areas close to the plant.

You can read the plan [PDF, 3.4 MB] or find out more on Newsline(external link).

Update on odour mitigation 

1 March 2024

An update report(external link) regarding the insurance process for the Christchurch Wastewater Treatment Plant was received by Council at the Finance and Performance Committee meeting on Wednesday 28 February.

The report contains all the information that can be released at this stage to keep the public informed without prejudicing our ongoing insurance claim or disclosing confidential commercial arrangements. The report confirms that design work to restore the trickling filters is underway and progressing well. Design work is due to be complete within the next two months.

At the meeting the Council acknowledged the community is continuing to experience odours from the Wastewater Treatment Plant. Our staff continue to address the recent increase in odour through a number of actions.   

The primary settlement tanks at the plant were previously identified as one of the main contributors of odour. To address this, we’ve now reduced the number of tanks in service from seven to five. As a result, sewage is now spending less time in in the tanks before it moves to the next stage of the treatment process. Early indications show this has reduced the odour from this source, and we’re planning on taking another tank out of service next week to improve things further.

Our external odour-specialist consultant is making good progress with their intensive odour monitoring programme and they’ve made a small number of recommendations for us to implement.

The trial at the temporary activated sludge plant is underway and being closely monitored to see if the addition of another aeration lane improves the performance of the temporary plant. It will take more time for us to assess if this has any benefits.

The oxidation ponds continue to operate well. Pond #1 now has all 16 aerators back in service. At some stage next week maintenance work requires us to briefly turn off all 16 aerators. We expect they’ll only need to be off for a couple of hours and we’ll plan this for a time where wind conditions are favourable for maintaining  the aeration of the ponds without assistance.

Aerators re-started to manage odours 

4 December 2023.

All available aerators on Oxidation Pond 1 have been re-started to minimise odours from the ponds. This decision was made following reports of odours in the area and monitoring showing reduced pond health.  

There may be some increased odour this afternoon as the aerators restart which will stir up the ponds. This should be short-lived, as there are winds forecast for tomorrow afternoon, which will further help rebalance pond health and minimise odours.

The aerators will ensure the ponds continue to stay healthy and function well.

The oxidation ponds are back to green

24 November 2023.

With summer on our doorstep, the ponds are showing signs of being very healthy. Our ongoing monitoring shows that Pond 1, the only one which was still classed as orange, now meets the criteria to finally turn green.

This also means that we're able to turn off several aerators, and we'll monitor the situation to see if they need to be re-started.

This also allows the contractor to do some regular maintenance over the summer period. This will involve bringing the aerators to the shore and taking them away for a service. We'll reinstate them back onto the ponds ready for autumn. 

We've also started the midge monitoring programme. Midge numbers are currently low, which reflects how well-established our midge control measures are, which we've progressively brought in since 2017. We'll continue to monitor the midge numbers, and bring in extra midge control measures if required. 

Insurance update

16 November 2023.

An update report on the Christchurch Wastewater Treatment Plant’s insurance claim for the November 2021 fire on the trickling filters has been provided to councillors. Read the full report.(external link)

The November 2021 fire was an unprecedented event that caused significant damage to two trickling filters at the Plant.

An update report regarding the insurance process, including investigations and the current position, was considered at yesterday's Finance and Performance Committee meeting (Wednesday 22 November).

This report contains all the information that can be released at this stage to keep the public informed without prejudicing our ongoing insurance claim or disclosing confidential commercial arrangements. Read more on Newsline.(external link)

Latest update

30 October 2023.

Two of the vertical shaft aerators on Pond 1 have stopped running. The contractor is aware of the issue, but the windy conditions mean they're unable to inspect and repair the aerators until Wednesday when the wind is forecast to drop. 

At the same time the current windy conditions, and warmer, longer days mean the ponds remain in good health, and we don’t expect the aerator break-downs will result in the ponds producing odours.

The remaining 14 aerators on the pond continue to operate.

On the night of Tuesday 2 October 2023, the arms of one of our two clarifiers at the wastewater treatment plant stopped rotating and were out of action for several hours.

These arms sweep the activated sludge off the bottom of the tank, and play a vital part in the treatment process - our temporary activated sludge plant requires both clarifiers to be running to achieve the current maximum flow through the plant.

Divers found three pieces of rubbish at the bottom of the tank, and since these have been removed, the clarifier arm has continued working. 

The findings of an independent review into the Council’s response and recovery from the wastewater treatment plant fire, and the Council's draft improvement plan, have also just been published with the Council's agenda for next week.  

The review highlights aspects where the Council did well and provides recommendations and suggestions where the Council could improve so that it’s better prepared to face other significant events in the future.

The draft improvement action plan identifies the need to work collaboratively with the local community, key partners and the local Waitai Coastal-Burwood-Linwood Community Board.

Read the Council report(external link) or independent review [PDF, 750 KB].

An update on the oxidation ponds

30 May 2023.

We've updated our situation(external link) page with an update on the oxidation ponds and the odours that are starting to get emitted from them as we head into the cooler winter period. We’re still trying to determine exactly what’s causing the smell, but we believe a combination of factors might be at play.

These include mechanical issues on the disc aerators, algae reducing considerably over the winter months, recent wet weather, and below-average settling floc earlier in the treatment process. Read more about each of these, and what our next steps are.(external link)

A return to all 'green' ponds

20 April 2023.

The 16 aerators we have installed on Oxidation Pond #1 are already making a significant difference to the biological health of the pond system. The aerator's performance is also exceeding the strict design criteria set by the Council staff.

Monitoring by both wastewater treatment plant operations staff and contractors is showing that all ponds are now recording higher dissolved oxygen levels, and visual observations are showing the ponds look healthier.

Observations of the aerators have also shown the initial sludge disturbance has settled down quicker than anticipated, with the water being aerated by the aerators running clear, with no ongoing sludge disturbance.

This has resulted in a negligible level of odours and hydrogen sulphide now being emitted by the ponds; recent monitoring had shown these levels were slowly beginning to increase over recent months.

All this means the ponds are now in a much healthier, robust position as we head into winter, and we’re able to turn all ponds to ‘green’ in the pond tracker(external link).

This rapid response in pond health, and the additional performance provided by the aerators, means the systems we’ve installed are more resilient, and the future risk of odours is now reduced compared to previous forecasts.

However, there will continue to be an underlying risk of odours present around the wastewater treatment plant until the permanent solution for the treatment process is completed.

Oxidation pond aerators are fully operational

 14 April 2023.

A project to minimise odours coming from the Christchurch wastewater treatment plant oxidation ponds has been successfully completed, with all 16 aerators surging to life yesterday. Read more on Newsline.(external link)

FENZ fire investigation report published

16 December 2022.

We have just received from FENZ their Fire Investigation Report – Shuttle Drive, Bromley, Christchurch City [PDF, 5.1 MB].

Consequently, we have not had an opportunity to consider it fully. Our own investigation is ongoing and we will not be commenting further.

Snapshot of hydrogen sulphide levels decrease

2 November 2022.

This graph shows how the hydrogen sulphide levels coming from the oxidation ponds has significantly decreased over the four months from 10 June to 10 October 2022.

The activated sludge plant was made operational on 28 July, with the biology reaching full maturity on 17 August, despite the challenges of growing the biology over the middle of winter. 

It took four weeks for the better-quality wastewater to flush through our network of six ponds, with the odour substantially reduced by mid-September. This was in line with the timeframes that we promised the community we'd work to.

Hold off from cleaning your house

30 September 2022.

With hydrogen sulphide levels dropping and the days warming up, it might be tempting to clean any discolouration off your house that might have been caused by a chemical reaction between lead paint and hydrogen sulphide. 

We ask that you keep waiting. Before we begin encouraging people to clean their homes, we'd like to see at least four weeks of low hydrogen sulphide levels and improved weather to get an idea of how any discolouration fades. 

We're about to start monitoring some 'test houses' and will provide updates on our website to show how the discolouration improves. 

If you absolutely must clean your house now, make sure you're familiar with our list of dos and don'ts that we published last month. 


  • Read the report findings and information(external link) on house discolouration. 
  • Wash your walls with a commercial chlorine-based solution, or warm, soapy water. This could help remove any organic dust, common moulds and some discolouration. The presence of these common moulds is not linked to the wastewater treatment plant fire.
  • Adhere to the manufacturers’ proprietary ratio recommendations if you use a commercial chlorine-based solution.
  • Several washes might be required.


  • Don't use a high-pressure washer to try and clean any staining or discolouration, as this could result in flakes of lead-based paint entering the environment.
  • Don't exceed the manufacturer’s proprietary ratio recommendations if you use a commercial chlorine-based solution.

The Ministry of Health(external link) has more information about lead-based paint.

Our team is keeping a register of homes that have reported paint discolouration. If your home has discolouration and you haven't let us know, or if you'd like more advice about what to do, email

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Meetings, minutes and reports

11 March 2024

Christchurch Wastewater Treatment Plant Odour Mitigation Plan [PDF, 3.4 MB].

7 July 2022

Christchurch Wastewater Treatment Plant  meeting between CDHB, ECAN and Christchurch City Council.

Action points:

  • Proceed with the setting up of the continuous monitors at the agreed sites.
  • Work with comms regarding the best way to display data on website from continuous monitors.

30 June 2022

Christchurch Wastewater Treatment Plant  meeting between CDHB, ECAN and Christchurch City Council.

Action points:

  • Circulate notes for confirmation
  • Circulate report on SIFT – MS sampling when available
  • Prepare draft/updated information for Council website.

23 June 2022

Christchurch Wastewater Treatment Plant meeting between CDHB, ECAN and Christchurch City Council.

Action points:

  • Send invitations to Medical Officer of Health for the Council meeting on 30/06

21 June 2022

Wastewater Treatment Plant Communications Advisory Group minutes [PDF, 592 KB].

9 June 2022

Christchurch Wastewater Treatment Plant meeting between CDHB, ECAN and Christchurch City Council.

Action points:

  • Report on Summary of completed sampling to be prepared.
  • Continue deploying H2S meters.
  • Ecan make available information from SO2 and H2S monitoring when available.