The latest on the stench
Christchurch Wastewater Treatment Plant update
Thursday 26 February
How we're communicating
We know these updates can feel repetitive. Many of you are dealing with the stench every day, and we understand that what you really want is for the odour to stop. That is our top priority.
We’re sending regular updates so we can stay in touch, be upfront about what’s happening onsite, and keep you informed about what our teams are doing to improve the ponds.
The odour can come and go, and people experience it differently across the city, so we want you to have up-to-date information as things change.
The latest on the stench
The ponds are much the same as earlier this week. The first three ponds are still not healthy, and this is showing up in our monitoring, which has recorded spikes in hydrogen sulphide levels.
The weather expected this week isn’t likely to help pond health. Shifts in wind and temperature can make odour levels increase, and we know many of you notice this straight away.
Our team continues to work on the ponds every day and respond as conditions change. We’re also making progress on longer‑term options, and we hope to share more about our next steps soon.
In the short term, we expect the odour will continue. It will vary depending on the weather, especially wind direction, and it may affect different areas at different times. The odour status map remains the same with six ponds at red and two at orange.
When we’ll be in touch again
We’ll send a brief update tomorrow to give you an idea of what to expect over the weekend. With pond conditions and the forecast as they are now, we don’t expect things to change much, so it’s likely there will be spikes of odour across the weekend.
A word from Gary
Thank you to everyone who came to talk with me at the Bromley Fair. It was really helpful to hear directly from residents about how the smell is affecting you, and what information you want from us.
After looking at the data from the door knock, I can see that the numbers we shared included both the people we spoke to in person and the follow‑up letters that were left in mailboxes.
I’ll now start revisiting the streets where we didn’t manage to speak with people directly, so I can gather more feedback. It’s clear that people are experiencing the odour in different ways, and I want to understand as many views as I can.
This week I’ve been busy setting up meetings with community members, including the local MP, and tomorrow I’ll be meeting with Pegasus Health.
I’m close to securing a part‑time office in the area so I can be more available for drop‑ins, and I’ll soon have a dedicated email address and phone number for this project.
I will be away from Wednesday 4 March to Tuesday 10 March for a wedding, but I’ll catch up on anything that comes through while I’m gone.
In the meantime, you can get in touch with me directly at gary.watson@ccc.govt.nz.
Why it smells more overnight and early in the morning
People have been asking why the smell can seem strongest overnight or early in the morning.
There are two main reasons:
- At night the air is still. Hydrogen sulphide is heavier than normal air, so when there is no wind and sun, the gas can settle and build up. When it does move, it moves slowly and can drift into nearby streets and suburbs at a higher concentration.
- The ponds produce less oxygen at night. The algae in the ponds normally make oxygen during the day, but they stop doing this at night. This means oxygen levels drop overnight, which can make odour worse.
This pattern is normal for oxidation ponds, but with the current conditions it means the spikes of stench overnight and in the morning are more intense.
How the jetboat works
There has been a lot of interest in why we're using a jetboat on the ponds and how it works. We're essentially using the jetboat (below) as a mobile aerator, which means it helps put oxygen back into the water.
It works in a simple way: the boat moves slowly back and forward. As it moves, it churns the water. This movement helps mix in oxygen, which supports the health of the ponds.
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.
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