Environment Canada says a special air quality statement has been issued for the northern Ontario cities of Sudbury and North Bay due to smoke from forest fires in the area.
The agency says smoke is causing poor air quality and reducing visibility, and warns conditions may deteriorate if the smoke descends to ground level.
The main source of the smoke is a fire known as Parry Sound 33 that has forced evacuations in parts of the municipality of Killarney, Ont., and prompted an evacuation alert in part of French River, Ont.
Parry Sound 33, which has burned through more than 100 square kilometres of forest, started on July 18 and is only five kilometres from the Trans-Canada Highway.
Ministry of Natural Resources spokesman Shayne McCool says Ontario Provincial Police are monitoring the highway to make sure smoke doesn't reduce visibility to unsafe levels.
McCool says the fire has not expanded since Tuesday, but the area has not received hoped-for rain that would have helped crews battle the blaze, which is listed as not under control.
"We were hoping to see some precipitation come and drop on that fire, but unfortunately we haven't seen a large amount," he said.
The fire has been less active due to high humidity levels and cloud cover allowing crews to "continue to make good progress in the containment areas of that fire," McCool said.
The ministry said there were more than 500 firefighters battling the blaze on Tuesday and McCool said about the same number were involved on Wednesday.
As of Tuesday evening, there were 41 active fires across northeastern Ontario and 101 fires in the northwest.
Ontario is receiving support from across Canada, the United States and Mexico as it deals with the fires, the ministry said.
There have been 914 forest fires in Ontario so far this year, compared to the 10-year average of 517 at this point in the season.
