There's a bug in the system that measures the air quality in Calgary. Literally.

A spider crawled inside the instrumentation at one of three monitoring stations, causing the machinery to give inaccurately high readings, according to Mandeep Dhaliwal, the air quality program manager with the Calgary Region Airshed Zone (CRAZ).

"This is one of those things that you never, ever expect to happen," he said.

"So that threw off the numbers for today's prediction.

"We're still having trouble getting the spider out," Dhaliwal added.

Both Environment Canada and Alberta Environment and Parks use the information from monitoring stations to calculate the Air Quality Health Index levels reported on their websites.

Long story short, the air quality reading for Calgary on Thursday is actually four — not "10+ very high risk" — as both government sites were reporting earlier.

The inaccurate readings couldn't come at a worse time, with all of southern Alberta — but especially Calgary — experiencing smoke-choked skies this week because of wildfires burning in the northwestern U.S. and British Columbia.

An air quality reading of four indicates a moderate health risk.