The Dunedin City Council has confirmed it is making changes at the plant after fielding 11 complaints since January about a foul odour emanating from the site.
Most of the complaints came from the neighbouring Chisholm Park Golf Club and nearby Tahuna Normal Intermediate School, whose staff complained when the wind carried the smell in their direction.
Golf club chairman Dave Watson said the smell could be ''fairly unpleasant, to say the least''.
He was pleased the council appeared to be working on the problem and hoped it would soon be resolved.
''Everybody's noticing the smell. It's an unpleasant odour that wafts on to the course from time to time. It depends which way the wind's blowing.''
Tahuna principal Tony Hunter said he first noticed the smell last year after four odour-free years at the school but it was worse this summer.
The school's operation was not affected, and neither were the pupils, but staff had been complaining about the odour.
''It's patchy. You don't smell it in some areas of the playground and it sort of comes and goes.
''Most of the time, even on a sunny day, we do have some sea breeze, so it tends to waft over here every now and then.''
Council wastewater treatment manager Chris Henderson said Dunedin's long, hot summer appeared to be contributing to the problem, by disrupting two of four biofilters used to cleanse odours at the plant.
The filters used irrigated layers of bark, gravel and seashells to encourage bacteria growth, which odours were then passed through to strip away smells, allowing only moisture and carbon dioxide to escape.
The result was supposed to be a ''musty bark'' smell, but hot weather meant maintaining the right moisture balance in the biofilters had proven difficult.
The biofilters' bacteria could start dying, allowing more odours to escape, he said.
The council planned to spend between $5000 and $10,000 improving the biofilters' irrigation system, and adding extra bark, and hoped to fix the problem by the end of the month, he said.
Other odour complaints had been received, but were traced back to different causes, including rotting sea cabbage at Andersons Bay inlet, a stock truck parked in the area and a composting operation nearby, he said.
The plant's odour problem was ''not significant'' for the facility, but ''public perception is a completely different thing'', Mr Henderson said.
''If there is odour, obviously I have an obligation to address it ... It's a significant concern to the surrounding people, but it's not actually a significant problem at the plant.''
