Christchurch Wastewater Treatment Plant update

Monday 23 February 

Weekend odour spikes 

We know many of you noticed spikes of stench across different parts of the city over the weekend. Thank you to everyone who took the time to report what you were experiencing – we understand this is frustrating, and we remain focused on both immediate actions and longer-term solutions.

The heavy rainfall last week has continued to affect overall pond health, and this aligns with the odours picked up both in the community and our monitors, where elevated hydrogen sulphide levels were recorded (see graph further down the newsletter).

We’ve also updated the odour status map to reflect the current conditions, with all but two ponds now sitting in the red category.

What we're doing

Our staff is actively responding to the changing conditions. This includes:

• Continuing hydrogen peroxide dosing to help lift oxygen levels and support the biological processes within the ponds.
• Running a sodium percarbonate dosing trial at the temporary activated sludge plant, with staff refining the approach as results come through.
• Working closely with specialist consultants on longer‑term improvements that will build greater resilience into the pond system.
• Monitoring key pond health indicators daily so that we can adapt quickly as conditions shift.

While conditions can change quickly – especially after significant rain – our teams remain focused on doing everything they can to stabilise pond health and reduce the likelihood of further odour events.

Avian botulism

We’re also carrying out work to manage avian botulism at the ponds, as we’re seeing some cases in the area. Our staff are working closely with our Parks team to respond quickly and minimise the impact on wildlife.

When we’ll be in touch again

We know odour events are frustrating and affect day‑to‑day life. We want to acknowledge that, and to assure you that improving conditions remains our priority.

We’ll send our next update on Thursday. In the meantime, our teams will continue working hard on site each day to support pond recovery and respond to changes as they happen.

There will likely be fluctuations in odour between now and then. Factors like weather, wind direction, and other environmental conditions can shift quickly, and these can influence how noticeable odour is at different times and in different parts of the city.

Bromley Fair 

He's grateful for the level of understanding shown by the community, and he’ll continue looking for opportunities to connect with residents over the coming weeks as he settles into his role and finds a local base to work from. 

In the meantime, you can get in touch with him directly at gary.watson@ccc.govt.nz.

Odour status 

There is a heightened risk of odour over the next week or so. We remain focused on doing everything we can to stabilise pond health and reduce odour. 

We’ll continue to monitor changes closely and update the map as conditions evolve.

Latest hydrogen sulphide monitoring 

The latest hydrogen sulphide graph shows that H₂S remains present at detectable levels. Our teams will continue to monitor readings closely and provide updates as trends develop.

Smelt it? Log it.

If you notice an odour, the best way to report it is by visiting smelt-it.web.app and logging what you’re experiencing – including location and strength. These reports help us build a fuller, more accurate picture of what’s happening across the community, so we can continue working to improve conditions.

Stay updated

We want everyone to be able to stay updated on what's happening at the Christchurch Wastewater Treatment Plant, and we regularly post new information on ccc.govt.nz/wastewaterfire 

You're welcome to send this update to your networks. If you know someone in the community who doesn’t have email or internet access, please print this newsletter off and pass it to them.

If you know of anyone who would like to receive this e-newsletter they can subscribe online. 

If you have any questions, or would like further information on the project, please call us on 03 941 8999 or 0800 800 169 or email wastewater@ccc.govt.nz  

Thanks for your patience and understanding. We’ll be in touch again soon.