Canadian wildfires burning across northern Manitoba and Saskatchewan are sending smoke through central Canada, the Great Lakes region and the northeastern United States, reducing air quality and visibility in major cities. Forecasters said they were “optimistic” that the lingering wildfire smoke would ease later in the day on Tuesday.

Smoke from fires across the West and Canada is causing potential health risks for people across the U.S. Satellite images show smoke from the wildfires in California is creating unhealthy air as far away as Las Vegas.