“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.

Smoke from Canadian wildfires hovered over several Midwestern states Saturday, bringing warnings of unhealthy air.

Smoke from wildfires blazing across Canada is once again wafting over huge portions of the Midwest and worsening air quality, with conditions particularly bad on August 1 in Minnesota, Iowa and Illinois.