Smoke from wildfires in Saskatchewan, Alberta and B.C are blamed for hazy conditions in parts of Ontario.
The fires may be thousands of kilometres away, but their effect is far reaching, drifting across the province.
The Ontario Lung association advising those with Chronic Lung disease, keep a close eye on air quality by checking your local Air Quality Health Index.
The OLA says check the index before taking part in outdoor activities, or strenuous exercise like running or cycling.
Smoke from forest fires contain carbon monoxide and tiny particles that can travel deep into the lungs, making it very difficult to breathe.
About 2.4 million live with respiratory issues like asthma or chronic obstructive pulmonary disease.
— OntarioLung (@OntarioLung) July 7, 2015