The cause of a foul odour that wafted over Pāpāmoa and Arataki from the Te Maunga Wastewater Treatment Plant in June will remain a mystery.

At the end of June, residents in the area took to social media describing the odour as “super disgusting”, saying it smelled as if sewage had seeped into their homes.

The Tauranga City Council confirmed shortly after that it was linked to operational issues at the plant.

Environment programme leader Jim Summers said at the time there had been “a discharge into the sewer network” that had “disrupted the biological processes used to treat wastewater” which triggered strong smells across surrounding suburbs.

Summers had said the council was unlikely to find out the exact cause.

Investigations into the discharge began immediately, but after three months the cause has still not been identified.

The Te Maunga Wastewater Treatment Plant is now said to be "operating as expected". Photo / Tauranga City Council

In a statement this month, Summers said the council investigation was complete.

“The council has been unable to determine the exact source or cause of the discharge.”

He said that given the volume of wastewater entering the treatment plant each day, it was not always possible to trace a discharge back to its source, and this had been the case this time.

“It is likely the discharge was of a high-strength chemical or waste product that should have been treated prior to entering the wastewater network.

“The plant has recovered well following the incident and is now operating as expected.”

Summers said treated wastewater continued to be discharged in compliance with consent conditions throughout the event.

“The council acknowledges the significant odour impacts experienced by residents in surrounding communities and appreciates their patience while the treatment system recovered and returned to normal operation.”

He said although upgrades to the Te Maunga Wastewater Treatment Plant would help to improve the resilience of the plant, the best way to prevent something similar happening in the future was for businesses to contact the council’s trade waste officers to discuss out-of-the-ordinary discharges to the wastewater network.

Ayla Yeoman is a Local Democracy Reporting journalist based in Tauranga. She holds a Bachelor of Arts majoring in communications, politics and international relations from the University of Auckland, and has been a journalist since 2023.

LDR is local body journalism co-funded by RNZ and NZ On Air.