Investigators from Southern California's South Coast Air Quality Management District received nearly 200 complaints about a "rotten egg smell" and began searching for the stench Tuesday morning, said spokesman Sam Atwood.
The odor is thought to be coming from the Salton Sea, a 376-square-mile saltwater lake about 150 miles southeast of Los Angeles, he told the Telegraph.
Atwood added that another theory has the smell coming from a wastewater treatment plant, but officials have yet to determine it.
"The odor was extremely intense," said Janis Dawson of the Salton Sea Authority. "We actually thought that somebody had an accident, a broken sewage main, that's how strong it was."
The dying, man-made Salton Sea is referred to as, has seen an increase in its salinity and is a major stopping place for migrating birds.
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The Salton Sea was created by accident in 1905 when a Colorado River irrigation canal flooded and spilled into a basin. According to the Telegraph, it's expected to become even saltier if it shrinks as expected by 2018.
Dawson noted that many fish in the sea have died off recently and strong winds have churned up the water, bringing bacteria to the top of the water possibly causing the foul smell.
The massive fish die-off has been blamed on low oxygen levels in the water and receding shorelines, according to reports.
A thunderstorm coming up from Mexico hit the area on Sunday, hitting the land around the sea with 60 mph winds.
"We were watching it from the office on our satellite radar and it was huge, one of the largest that any of us have ever seen in probably 10 years," the Telegraph quoted Mark Moede, a National Weather Service meteorologist in San Diego.
Official said the smell poses no health hazards.
"The Valley is starting to smell like rotten eggs. In an unrelated note, Febreeze sales are through the roof in the San Fernando Valley," Jose Chavez, a 28-year-old comedian who lives in the area, joked.
"My first thought was that maybe one of the eggs I bought was rotted and I got back home and the smell was still there so then I started to think it was me so I changed my clothes," he said. "It was very pungent."