Smoke from the explosive forest fires in northern Minnesota drifted into parts of eastern Canada on that day . Environment Canada flagged areas in Ontario among the worst globally for air quality on some days . Southern Ontario’s major cities faced urgent warnings about hazardous air from the drifting haze. Extreme drought and howling winds helped blazes spread at breakneck speed through Minnesota and nearby states. Polluted haze drifted north, blanketing Canada in a persistent layer of contaminants.