Mayor Pat Fiacco issued a formal apology Wednesday to residents affected by the smell that is wafting into the west and northwest ends of the city.
Warm temperatures, aging infrastructure and low oxygen levels in the lagoons are being blamed for the problem.
Fiacco says chemicals are being added to the wastewater in an effort to reduce the odour in the short term.
He said a broken blower that pumps oxygen into the water is expected to be up and running by the end of the month.
The city plans to upgrade the wastewater treatment plant by the end of 2016 to meet new provincial and federal regulations.
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