Some of the worst air quality in the world sits over Ontario Wednesday

Ontario is grappling with some of the world's poorest air quality Wednesday due to wildfire smoke.

By the morning hours, Toronto was ranked first, with conditions expected to deteriorate further throughout the day.

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A wildfire outbreak earlier this week in northern Ontario continues to drive extreme fire activity.

Dry conditions and intense heat—peaking at 38°C in Sioux Lookout and 40.8°C in Armstrong on Tuesday—have resulted in a high to extreme fire danger. Hundreds of uncontrolled wildfires are sending thick plumes of smoke into the air.

PHOTOS: Blanket of wildfire smoke creates eerie skies in Ontario and Quebec

Evacuation orders remain in effect for Armstrong and Whitesand.

Some relief may come Friday into Saturday, as a weather system moving along the international border could bring 5-20 mm of rain. Temperatures are expected to cool into the mid-20s by week’s end.

RELATED: Accommodations fill up as wildfires spur more evacuations in northwestern Ont.

Smoke from northern Ontario wildfires has spread over 1,000 km, with the jet stream carrying it southeast. Hazy skies, diminished sunlight, and a smoky odour have been reported.

The wildfire smoke even reduced the severe storm threat in eastern Ontario and Quebec on Tuesday.

By Wednesday afternoon, wildfire smoke will cause very poor air quality conditions in southern Ontario, including the Greater Toronto Area (GTA), Windsor, and Ottawa.

DON'T MISS: The Weather Network's hub for all wildfire information in Canada

Smoke is expected to linger through much of Thursday, as it expands across the U.S. northeast, including New York City and Washington.

Conditions will gradually improve in eastern Ontario Thursday afternoon, and across southern Ontario by Friday.

Impacts include increased health risks for those with respiratory issues, hazy conditions, and visibly red sunrises and sunsets. Outdoor activities should be limited until air quality improves.

Smoky skies observed in Cornwall, Ont., on July 14, 2026. (The Weather Network)