“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.

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.

A stretch of southern Ontario remains under a special air quality statement today amid smoke from wildfires burning in parts of the country. Environment Canada says smoke from forest fires can cause reduced air quality and visibility that can fluctuate throughout the day.