The smoke is expected to remain over the northern and central Plains of the United States for the next couple of days, according to meteorologists.

Smoke from forest fires in the Prairies will affect southern Ontario Wednesday night, Environment Canada says. The statement came just as the weather agency lifted the city's fifth heat warning this year.

Toronto’s air quality index was at eight, or “high risk,” this morning. Environment Canada says reduced air quality can cause mild eye, nose and throat irritation while more serious but less common symptoms include chest pains and a severe cough.