She said some areas of Wanganui were badly affected by the smell yesterday and Monday.
"Wind direction and strength make a huge difference to which areas are affected and how strong the smell is. A strong wind dissipates some of the smell, but in a light breeze it hangs in the air.
"It is particularly bad in a south-easterly breeze."
The council's senior wastewater engineer, Arno Benadie, said the odour neutralising system around the pond was now completed, and bio-augmentation was continuing.
"Bio-augmentation involves growing good bugs and injecting them into the pond where they reduce the level of sludge. The testing showed it was healthy, digested sludge so the bugs are working as they should."
But Mr Benadie said this process would take some time, as the layer of sludge is about 3 metres deep. He warned there may be more stench coming from the ponds today as engineers try operating some of the aerators in the deepest part of the pond to increase the level of oxygen.
"However, this may cause sludge to be dragged to the surface, causing more odour."