The Lake Tahoe region, the natural getaway for generations of visitors from California's urban coast, is in the midst a terrible air quality.
On Wednesday, Purple Air, a company that sells home air quality monitors and publishes regional results from the resulting virtual network reported that the area had the worst air quality in the world.
Earlier, the federal air-quality data site AirNow reported a US Air Quality Index peak of 422 for South Lake Tahoe. That puts the air near the freshwater lake in the Sierra Nevada Mountains in the "hazardous" range.
"It's some of the worst air we've seen there," said Amy MacPherson, spokeswoman for the California Air Resources Board.
The last time the area experienced anything near this week's smoke, she said, was during the Rim Fire, which burned for weeks in late summer 2013.
MacPherson said a forecast of shifting winds could probably improve things by the weekend. The National Weather Service also said in its forecast discussion on Wednesday that air quality could improve by the end of the week.
The Caldor Fire, which began on August 14 in the Grizzly Flats area of El Dorado County, is the state's third-largest blaze. Earlier, the California Department of Forestry and Fire Protection said that it was 11 percent contained.
On Tuesday, Gov. Gavin Newsom said that the White House has approved a disaster declaration, which comes with federal funds, for nearly a dozen wildfires in California.