Dense smoke blankets southwest Bend in August. (Julia Shumway/Bulletin photo)

The heavy smoke that smothered Bend on Tuesday afternoon came from the Milli Fire near Sisters and two wildfires west of the Cascades, agencies fighting the fires confirmed.

Deschutes National Forest spokeswoman Kassidy Kern said the Rebel and Whitewater fires contributed to dense smoke in Central Oregon.

“Unfortunately, we’re bearing the brunt of it because of the wind directions,” she said.

The Oregon Department of Environmental Quality rated air quality at the Bend pump station as unhealthy for sensitive groups beginning around 3 p.m. Tuesday. People with heart or lung disease, older adults and children should reduce outdoor exercise, and everyone else should limit prolonged or strenuous outdoor activity.

Bend’s air quality was considered good earlier in the day, department spokesman Greg Svelund said.

“It was green until 1 or 2 p.m.,” he said. “That’s when it really started turning. Even now, as bad as it is, we’re probably headed to an advisory in the morning.”

The department closely monitors air quality but is conservative with hazardous air warnings, he said. Conditions can change rapidly because of factors including temperature, wind and the location and severity of wildfires. In Bend, it can be difficult to predict smoke conditions from hour to hour, he said, but if heavy smoke conditions persist Wednesday morning, the department will consider issuing a warning.

High school practices for fall sports, including football, cross-country and soccer, can be affected by the smoke. Coaches have to adjust their practices based on air quality, Mountain View High School athletic director Dave Hood said, but they also consider shifts in the wind.

“You have to err on the side of caution for the kids,” Hood said. “We’re day-to-day, almost hour-to-hour, looking at it.”

Bend High School coaches canceled water polo practice Tuesday evening because of the poor air quality, and the Summit High School football team practiced indoors at Bend’s Boss Sports Performance to avoid smoke.

The Milli Fire, which began Aug. 11 a few miles west of Sisters, had burned 11,236 acres and was 23 percent contained by Tuesday.

The Rebel Fire has burned close to 3,000 acres in the Three Sisters Wilderness since Aug. 4, and the Whitewater Fire has burned almost 8,500 acres in the Mount Jefferson Wilderness.

Heavy smoke in Sisters also grounded firefighting aircraft at the Milli Fire on Tuesday. The smoke stifles fire’s access to the oxygen it needs to grow, so firefighters don’t expect the Milli Fire to spread much.

— Reporter: 541-633-2160; jshumway@bendbulletin.com

— Bulletin reporter Kailey Fisicaro contributed to this article.