Residents in Port Tennant claim the odour from the Welsh Water plant on Fabian Way has become so bad it can be "tasted".
Swansea Eastside Against The Smell is calling for the company to fix the issue.
Welsh Water has apologised to residents and said it is investigating the cause.
The company is holding an information event at the treatment works on 25 November so residents can hear about plans to resolve the problem.
Resident Andy Smith, 53, who founded the group, said: "The smell gets into everything. We have to light candles in the house to make the smell go away. Welsh Water needs to rectify the problem."
Councillor Joe Hale, whose ward covers the area, said the problem has been going on "for a number of years" but residents are "getting to the stage where enough is enough".
"It's no exaggeration when there are emissions you can taste it. It's disgusting," he added.
Welsh Water said it has stopped using the site's digester plant, used to convert sewage gases into renewable energy, and has introduced extra treatment to the processes to help mask the smell.
"Whilst unpleasant, the smell does not pose a danger to health. We would like to reassure anyone affected by the odours that we are investigating the cause," a spokeswoman added.
"Welsh Water has invested significantly in measures to help address these odours and we are committed to solving these odour problems as quickly as possible."
A "disgusting" smell of sewage from a water treatment works in Swansea has led affected residents to form a new campaign group.