Environment Canada has issued a special air quality statement for Niagara.
They say they hot and humid weather has created elevated pollution levels.
Officials say the increase in ground-level ozone concentrations are expected to create poor air quality for the next few hours.
Higher pollution levels are expected to persist this afternoon through this evening.
People are being advised that you may experience symptoms such as increased coughing, throat irritation, headaches or shortness of breath.
Children, seniors, and those with cardiovascular or lung disease, such as asthma, are especially at risk.