DULUTH – The encroaching wildfires from Canada continue to threaten the borders of the Boundary Waters Canoe Area Wilderness and worsen air quality throughout the state.

The Minnesota Pollution Control Agency on Tuesday extended its air quality alert to most of the state through Thursday morning.

Heavy smoke from several wildfires in Ontario and Manitoba traveled into northern Minnesota overnight, and its fine particle levels are ranked "very unhealthy" for everyone across north central Minnesota, the agency said in a news release.

Meanwhile, forest rangers are sweeping through areas of the Boundary Waters that closed over the weekend to find campers and hikers and offer guidance and warnings of possible danger. Travel times to these areas "are measured in days, not hours, and this would not allow for rapid evacuation of the area," the U.S. Forest Service said in a news release. The Superior National Forest announced new entry point closures on Saturday, citing the potential for three fires to spread across the Canadian border from Quetico Provincial Park.

The National Forest's expanded closure order says recent reconnaissance flights conducted by fire managers showed increasing fires despite lighter winds, and "fuels in this area are preheating and becoming more volatile."

"They are very large fires, and with the dry conditions Ontario is experiencing … there is a lot of concern," said Cecile Stelter, a public information officer for the interagency team managing the U.S. response to the area's fires, which is working with its Ontario counterparts. She noted the recent low pressure system that passed over the area didn't cause any significant movement of the fires toward the U.S. border.

The Canadian fires could head into the Crooked Lake travel corridor and beyond, into more heavily visited areas of the Boundary Waters, fire managers said Tuesday, and daily flights monitor those fires. Quetico has closed the southwest portion of the park, adjacent to Crooked Lake. The widespread drought has contributed to extremely dry fuel for wildfires, Stelter said, much drier than past years.

"People really need to take this seriously," she said, and call ahead to outfitters if they have travel plans in the area.

Forest employees are staked at closed entry points to redirect paddlers and other visitors and have posted closure signs.

The Delta Lake fire that began earlier in July, 19 miles east of Ely in a blowdown area, spans 62 acres and is 35% contained with "slow and steady mop-up," according to a news release from the Eastern Area Incident Management Team. A handful of other fires scattered throughout the Boundary Waters are contained but continue to be monitored. Some Boundary Waters entry points, lakes and portages around Delta Lake remain closed and a ban on campfires throughout the wilderness area and in most of the Superior National Forest remains in place.

Jana Hollingsworth • 218-508-2450