A special air quality statement has been issued for southern Ontario as smoke from fires has moved over the area.
Environment Canada says high levels of air pollution are possible due to smoke from ongoing forest fires in northwestern Ontario.
Elevated particulate matter levels and hazy conditions have been reported at several stations.
Reduced visibilities and deteriorating air quality are possible if the smoke descends to ground level.
Conditions are expected to improve Tuesday with the passage of a cold front.
People 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.