Smoke from more than 700 active Canadian wildfires continues to drift south and east, pushing air-pollution levels across large parts of North America to their worst readings of the year. Minneapolis and Chicago briefly ranked among the most polluted major cities in the world over the weekend, with IQAir reporting fine-particle (PM2.5) concentrations of 134 and 105 respectively. The U.S. National Weather Service and state agencies have issued air-quality alerts from Minnesota to Connecticut, warning that conditions are now "unhealthy" for sensitive groups and, at times, for the general public. New York City, Boston and Philadelphia recorded sharp drops in visibility on 4–5 August, while Toronto remained under an Environment Canada statement for a third straight day. Authorities urged residents—especially children, older adults and people with heart or lung disease—to curtail outdoor activity and use filtered indoor air when possible. Environment Canada said parts of Manitoba, Saskatchewan and northern Ontario recorded Air Quality Health Index readings of 10 or higher—its most severe category—after a high-pressure system forced smoke to the surface. The agency’s forecasts show hazy conditions lingering through the week as fresh fires flare and winds shift. The Canadian Interagency Forest Fire Centre counts more than 16 million acres burned so far this season, making 2025 the second-worst year on record after 2023. Roughly two-thirds of the blazes remain out of control, stretching firefighting resources and complicating efforts to safeguard communities and key infrastructure. The cross-border haze has prompted political friction. U.S. Representative John James of Michigan asked Prime Minister Mark Carney to strengthen forest-management policies, calling the smoke a "public-health emergency," while Wisconsin legislator Calvin Callahan lodged a formal complaint with the U.S. Environmental Protection Agency and the International Joint Commission. Manitoba Premier Wab Kinew dismissed the criticism as a "timber tantrum" and thanked U.S. firefighters assisting Canadian crews.