Canada is facing a wildfire catastrophe of historic proportions. Blazes sweeping across Manitoba, Saskatchewan, and Alberta have forced over 33,000 people to flee their homes, marking one of the largest evacuations in the country’s history.

Smoke from wildfires burning in three Canadian provinces covered about a third of the U.S. on Wednesday, forecasters said, but had little effect on air quality except in New England and parts of New York state and the Midwest.