Authorities are investigating a “mystery odor” that filled the air in Delaware, Pennsylvania, and New Jersey over several months.

Locals have been consistently calling multiple agencies, power companies, and officials in the tri-state area with regard to the strange smell akin to that of some fuel. Officials are trying to ascertain whether the smells being reported in the three states and the neighboring areas are connected, Delaware Online reported.

The task of finding out whether the smell has a common source made the investigation all the more challenging.

The smell, however, has transitory existence. "Once the odor’s gone, it’s almost impossible to figure out where it came from," Virginia Cain, a spokeswoman with the Pennsylvania Department of Environmental Protection said.

In December, Delaware County Police Department had created a special task force to solve this looming mystery once and for all. Locals in Brookhaven, Pennsylvania, complained about a strange smell of sewage and horse manure rolled into one. The special task force deemed the smell to have erupted from a petroleum-based product, insisting the alleged source was a five-mile stretch along the Delaware River from Tinicum to Marcus Hook, according to a report by 6 ABC.

Cain also hinted at the nearby industries along the Delaware River as being the source of the smell. She said the smell people have encountered while passing through northern Delaware or nearby New Jersey may have been carried by the oncoming wind. She said they will deploy an RV-like vehicle to analyze and sample the air around Delaware County and nearby facilities to get at the bottom of it.

The coalition's volunteers collected nearly half a million pieces of plastic waste during a coordinated 'World Clean Up Day'
The coalition's volunteers collected nearly half a million pieces of plastic waste during a coordinated 'World Clean Up Day' AFP / Luis ACOSTA