The smell of sewage is wafting over Nelson again, as warmer weather upsets treatment ponds north of the city.
Nelson City Council said the odour was caused by bacterial breakdown of oxygen-starved sewage in oxidation ponds at Nelson North Wastewater Treatment Plant.
Councillor Stuart Walker said it was a disappointing recurrence of the problem, which the council had thought was under control.
The last time the stench hit, the council was found to have breached resource consent conditions over the smell.
The firm contracted to run the plant said it was working to help the ponds recover.