Christchurch Wastewater Treatment Plant update

Wednesday 28 January 

Odour from Christchurch Wastewater Treatment Plant ponds

You will have noticed an increase in odour from the Christchurch Wastewater Treatment Plant’s oxidation ponds. Unfortunately, over the coming week, there is a high likelihood the increase in odour will continue.

We understand how frustrating and unpleasant this is, and we’re doing everything we can to manage the situation. If you’re concerned about the impacts of the odour there is a range of information on our website about odour and health, and what support is available for impacted residents.

What's happening in the ponds 

The recent period of heavy rain has significantly affected the health of several oxidation ponds. Monitoring from this week showed a drop in dissolved oxygen (DO) levels across the system. These low‑oxygen conditions create an environment where odour is much more likely to be released, particularly from Ponds 1, 2 and 3, which are currently the most affected.

This is different from what we’ve seen in the past. During previous wet‑weather events, the additional rainfall has generally supported pond recovery, improving overall pond health and preventing odour issues. However, this time the ponds have not responded in the same way. Our staff are continuing to collect and analyse data to understand why these conditions have developed on this occasion.

We’ve also seen increased loading to the ponds. These factors also put more pressure on the ponds, increasing the likelihood of odour.

What we're doing 

Our operations teams are closely monitoring conditions and responding wherever possible to improve pond health and minimise odour. This includes:

• Adjusting flows through the ponds to stabilise loading.
• Regular monitoring so we can react quickly to changes.
• Using all available operational tools to support oxygen levels and improve pond performance.

We know odour impacts are disruptive, and we want to reassure our community that reducing them is a priority for us.

What to expect 

Based on current pond health, we expect higher‑than‑normal odour levels may continue for at least the next week. We’ll keep providing updates as conditions change. Thank you for your understanding and patience as we work through these challenges.

Latest hydrogen sulphide monitoring 

The biological health of the ponds is still fragile. Intermittent levels of odour are being detected at community monitoring sites. 

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.