A strong and unpleasant smell has been noticed across parts of Christchurch, with chrislynchmedia.com readers messaging in saying the odour across the city was particularly bad.

The Christchurch City Council said the smell was coming from the Christchurch Wastewater Treatment Plant oxidation ponds and warned the odour was likely to continue over the coming week.

A council spokesperson said recent heavy rain had significantly affected the health of several oxidation ponds, leading to conditions that increased the likelihood of odour being released.

“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,” the spokesperson said.

The council said monitoring showed a drop in dissolved oxygen levels across the system, creating low oxygen conditions where odour was more likely to be released, particularly from ponds 1, 2 and 3.

The spokesperson said this event differed from previous wet weather periods, which had usually helped the ponds recover rather than worsen conditions.

“This is different from what we’ve seen in the past. During previous wet weather events, the additional rainfall has generally supported pond recovery. However, this time the ponds have not responded in the same way,” the spokesperson said.

The council said increased loading to the ponds had also added pressure to the system, further increasing the chance of odour.

Operations teams were closely monitoring conditions and taking steps to improve pond health and reduce the smell, including adjusting flows, increasing monitoring, and using available operational tools to support oxygen levels.

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

The council said higher than normal odour levels were expected to continue for at least the next week, with updates to be provided as conditions changed.