Midge numbers up at oxidation ponds

The recent wet weather has had a positive impact on the biological health of the ponds. The volume of rain means wastewater entering the plant hasn’t been as strong, and as a result algae are flourishing.

Algae helps the pond system operate well by generating oxygen within the ponds and preventing the anoxic conditions which can cause odour. We’re still waiting on odour monitoring for the holiday period but we are anticipating that this will show a decrease in odour coming from the ponds which were a source at the end of last year.

Algae are also a food source for midges and the increase in algae has resulted in a surge in the number of midges on and around the oxidation ponds, with numbers much higher than the previous few summers. If you’ve been past the ponds recently you might’ve noticed an increase in birdlife, which has also been recorded by Council ecologist Andrew Crossland. This increase in bird numbers has been linked with the increase in midge numbers, as the midges and their larvae are a food source for aquatic birds.

We have a midge control programme in place which includes native planting around the oxidation ponds. Native plants encourage midges to stay close to the ponds rather than spreading to local residential and commercial areas. Since 2018 we have planted approximately 75,000 native plants around the oxidation ponds.

In the past, when the ponds were healthy, we dredged the bottom of the ponds and altered the flow paths through the ponds to reduce midge numbers. We’ve considered these control options but have decided against them at this time as there is a real risk of disturbing and unsettling the health of the ponds, which could generate odour.

We’re monitoring the situation closely and will continue reviewing what midge control measures can be put in place. We know the midges can be frustrating and are grateful for the patience of local residents.

Trickling filter demolition update

After a break over the holiday period Southern Demolition are back on site. Great progress was made before the break with the walls of both trickling filters to ground level and the demolition of the foundations underway.

Since returning from break, trickling filter one has had its internal pillar demolished and progress is being made on demolishing its foundation. The demolition of the foundations continues and will be the focus over the next few weeks.

The photo below was taken on 9 January 2025.  

Stay updated

We want everyone to be able to stay updated on our response and recovery from the treatment plant fire, and we regularly post new information and reports on ccc.govt.nz/wastewaterfire 

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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.