Smoke from the blazing Minnesota fires in northern Minnesota drifted into Ontario 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 distant fires . Prolonged dryness and fierce gusts helped blazes spread at breakneck speed through Minnesota and nearby states. Toxic smoke drifted north, blanketing Canada in a thick veil of contaminants.