Canada is battling more than 700 active wildfires across the country, roughly two-thirds of which are burning out of control, according to the Canadian Interagency Forest Fire Center (CIFFC). Smoke billowing from the blazes has blanketed central Canada and the northern U.S., prompting widespread air quality alerts.

“Air quality and visibility due to wildfire smoke can fluctuate over short distances and can vary considerably from hour to hour,” Environment and Climate Change Canada (ECCC) said in its statement.

Environment Canada has issued special air quality statements for southwestern Ontario as prairie wildfire smoke sits over swaths of the province.