Late last night, according to SFist readers and KCBS, San Francisco was blanketed with a malodorous odor, stretching all the way from the Outer Richmond to the Financial District to the Excelsior.

One readers reported: "Dude, San Francisco smells like shit all of a sudden. Sure none of the sewers are leaking? Maybe a citywide Marijuana pot growing operation? Unannounced bug spray?"

And another griped: "Ugh, why does the entire city smell literally like shit right now? From the Financial District to the Inner Sunset, it smells like a freshly-fertilized field from my Wisconsin youth.

Again: "OK, according to Twitter, I'm not going crazy. People in the Marina and Excelsior are smelling it, too."

And: "I smelled it too in the Inner Sunset. I walked outside this afternoon and started dragging my shoes thinking I'd stepped in something. It's really really foul. It seemed worse when I was walking west and the wind was blowing off the ocean than when I was coming back east and there was less breeze."

According to KCBS, calls came in from the Sunset and Richmond districts reporting the stench. "A city spokesman said the sewage treatment plant didn't report having any problems and that everything appeared to be functioning normally. A Public Utilities Commission spokesman did say that he smelled something unusual in the Civic Center area."

A couple of theories, suggests KTVU: the cleaning sewer lines near Mission Bay, and "a red tide or algae bloom along the coast that might be the culprit."