An unpleasant and mysterious odor has lingered in southwest Washington state, wafting over multiple communities overnight.

Cowlitz County Emergency Management Services began to field 911 calls from residents about the smell around 6:30 p.m. on Tuesday, according to a statement obtained by USA TODAY. 

The smell, according to Cowlitz County, seemed to have wafted through South Kelso, Rose Valley, Kalama, Woodland and Cumbia County before it hit Portland. 

“The source of the odor and what the odor is/was, are still unknown and under investigation,” Cowlitz County wrote.

A couple of theories have emerged in the hours since the smell was first reported, according to the county, including a “ship, train, highway transportation leak; Scappoose Bio Solids; industry; pipelines; natural gas; Mt St Helens; and ground movement.” 

“Complaints have varied from unpleasant odors to minor health issues. All agencies continue to work on the situation,” according to Cowlitz County EMS.

Unpleasant odor complaints vary, have been ‘very inconsistent’

Wind conditions, according to Cowlitz County, were “variable” in direction and speed up until 6 p.m., moving outside of the north and northwest part of the region from Longview towards Portland gradually.

Multiple Cowlitz County agencies responded to odor complaints made in the area as a result of the wind’s path starting Tuesday evening. 

Cowlitz County EMS were working with both local and federal agencies to figure out the cause of the odor. Even the National Weather Service has weighed in on the matter, mapping the path of the “strange smell” on social media. 

“By tracking winds, we can estimate the path that it may have taken, briefly drifting down near Vancouver WA before southerly winds around 4AM would have pushed it back north again.”

Cowlitz County EMS noted that the identification of the smell was “unusually very inconsistent.” 

“Descriptions have varied from, similar to natural gas, propane, burning garbage, burning rubber, ammonia, and others. As of this briefing, complaints have varied from unpleasant odors to minor health issues.” 

No ‘abnormal activities or readings’ from Mount St. Helens

Cowlitz County EMS checked the Cascades Volcano Observatory to see if there was a connection between Mt. St. Helens and the reported odor. 

Some residents have even wondered if the source of the odor is tied to Mount St. Helens or volcanic activity in some way. 

“Given the sulfur smell people have described and no known origin at this point as well as the widespread sensation, I’m wondering if it could be volcanic in nature,” one user wrote under the National Weather Service’s post. 

Another asked, “what’s up with Mt St Helen’s ?? anyone @MtStHelensNVM that makes the most sense yall anyone seismic stuff going on.” 

But, according to The Cascades Volcano Observatory, there have been “no abnormal activities or readings” in air quality and seismic activity coming from Mt. St. Helens as Tuesday night through Wednesday afternoon. 

Residents have taken to social media to express their thoughts and feelings about the situation, writing in X and Facebook comments that the smell was "weird" and "strong." Others wondered how dangerous the odor really was and why officials failed to provide a concrete answer about the odor and where it came from.