Christchurch City Council has said wastewater ponds are transitioning into winter mode, with cooling temperatures slowing biological activity across the system.

A spokesperson said overall pond health remained stable despite seasonal changes.

“Water temperatures across the ponds are slowly cooling, which is a clear sign that the system is transitioning into winter mode,” the spokesperson said.

The council said changes in temperature and daylight can affect how the ponds look and perform, even when the system is operating as expected.

“As temperatures drop, the biological processes in the ponds slow down, which can change how the ponds look and perform,” the spokesperson said.

Efforts to increase aeration are now underway following a council decision last week, with further updates expected once planning is complete.

“As we head into the weekend, pond health remains stable, with no changes to the current odour status,” the spokesperson said.

The council said odour levels follow a seasonal cycle, with the greatest risk typically occurring during transitions between seasons.

During summer and winter, odour is usually low due to more stable biological conditions.

In warmer months, algae growth helps produce oxygen, allowing beneficial bacteria to break down wastewater more efficiently and limit smells.

As conditions shift into autumn and spring, reduced sunlight and changing biological activity can temporarily increase odour.

The council said these fluctuations are expected as part of the natural cycle of the treatment process.