Multiple agencies say they are investigating the foul odor.
The smell -- which some have described as a combination of "The Walking Dead," rotten eggs and burning tires -- remained unmistakably detectable on Friday morning.
A Los Angeles County Fire Department hazardous materials team was seen near the channel, investigating what an agency spokesperson said was an "unknown odor" emanating from the waterway.
The spokesperson said investigators have not found any evidence that the unpleasant smell is caused by something particularly dangerous or an emergency.
It is, however, at best uncomfortable for people who live in the Carson area and have experienced the relentless odor since Monday. Some have told ABC7 that they suffered nausea and other symptoms as a result.
"I lost my appetite. It's giving me bad headaches," said a resident named Twila, who declined to give her last name. She mimicked a gagging sound while describing the reaction of herself and her coworkers. "It's bad," she said.
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"According to the security personnel at the Marathon refinery, the fenceline readers are reading normal and no special processing is currently occurring at refinery," the South Coast Air Quality Management District, which is also investigating the matter, said in a Thursday statement.