From Edgewater to Roscoe Village to Beverly, Chicagoans have said they’ve been smelling similar wafts of sewage this month. Online, a Reddit user said they were getting “gross, fishy wafts of stank” outside of a West Loop McDonald’s last week.

The culprit: Lack of rainfall, said Megan Vidis, a spokeswoman for the Chicago Department of Water Management.

Most of Chicago, along with about 50 suburbs, uses a combined sewer system, Vidis said.

This means rainwater and wastewater from houses pass through the same pipes on the way to the Water Reclamation District, where the water is purified and released back to waterways, Vidis said.

When there’s less rain — and a higher concentration of wastewater in the system — the stench of sewage wafting through the city is a natural outcome, Vidis said.

Right now the area “doesn’t have the rainwater to dilute [the wastewater] and make it flow faster through the system,” she said. “That’s how it works. It’s pretty simple. We get these calls every year when it hasn’t rained for a while.”

The city has only had 0.04 inches of rain in September, according to the National Weather Service. The monthly total average is 1.73 inches.

Prolonged periods without rain can be a contributing factor to sewage smells in the city, confirmed Kevin Fitzpatrick, the assistant director of engineering for the Metropolitan Water Reclamation District of Greater Chicago.

Chicagoans should report any odors to the Metropolitan Water Reclamation District, said spokesperson Allison Fore. People can fill out an online complaint application or call 800-332-3867.

The good news for those tired of the stank: Rain is in the forecast next week.