Parts of Canada and the US Midwest have issued air quality alerts due to the amount of smoke from wildfires, with some areas on Tuesday experiencing some of the worst air quality levels ever recorded.
After the east coast was covered earlier this month, smoke has been spreading southward across North America in waves.
The Canadian Interagency Forest Fire Centre claims that this year's wildfire season is the worst on record in Canada.
On Tuesday, the area was covered in a burning smell and visible haze, and several cities, including Chicago and Milwaukee, as well as areas of Michigan and Ontario, recorded air quality index levels in the 200s on a scale of 500.
Although slightly lower than earlier this month's levels, which exceeded 400 in some parts of the eastern US, those numbers are still regarded as "very unhealthy.".
When the air is unhealthy, people should limit their outdoor activities, especially vulnerable populations like children, the elderly, and those with respiratory conditions, according to health authorities.
On Tuesday, summer programs would be held indoors, according to Chicago school officials.
Almost 500 of the nearly 3,000 fires that have been reported so far this season, according to Canadian fire authorities, are still burning. 7.7 million hectares (30,000 square miles), or about the size of South Carolina, have already been burned down.
According to the European Union's Copernicus Atmospheric Monitoring Service, the fires have released an unprecedented 160 million tonnes of carbon into the atmosphere.
Over the next few days, it is anticipated that the smoke will move to the south and east.