This is a carousel. Use Next and Previous buttons to navigate

Contra Costa firefighters battle the Marsh Fire in Pittsburg on July 9.

Contra Costa firefighters battle the Marsh Fire in Pittsburg on July 9.

A stubborn fire in Contra Costa County wetlands that burned for weeks during the summer, periodically pushing acrid smoke across the region before it was finally extinguished by flooding the area, has started to smolder again, fire officials said Sunday.

While air quality was in the “acceptable” range Sunday, county health officials said they were monitoring the situation and would alert residents if conditions changed.

The Marsh Fire ignited in late May at a homeless encampment at Marsh Creek Road and Walnut Boulevard in Pittsburg. No injuries were reported, but the fire totally consumed the encampment and over the next six weeks burned into large amounts of peat and brush in an area mostly inaccessible to fire crews because of the unstable soil.

The fire spread through more than 500 acres, causing smoky skies and unhealthy air quality levels, with flare-ups that forced evacuations and threatened a power plant.

Finally, fire officials and the property owner put out the flames in mid-July by flooding the land at a rate of 1.2 million gallons of water every hour.

“No apparent hotspots or smoke remain, though we continue to monitor for flareups,” the Contra Costa County Fire Protection District tweeted on July 23.

But fire officials on Sunday confirmed to The Chronicle that the fire began burning again in early September.

“Apparently a small part has started to smolder again,” said Tracie Dutter, assistant fire chief of the fire district.

Such behavior is not uncommon for peat fires, Dutter said. “It is not to the extent that it was during the summer a couple of months ago,” she added. “It’s possible that we get involved again, but at this point, it’s not an emergency.”

The area that started to burn again, Dutter explained, is the highest elevation of the land that doesn’t have a levee system — meaning it was impossible to flood that area.

As of Sunday, the fire district had not sent out firefighters to the area. Dutter said the property owner has “stepped up at our request” and hired a private water tender, who has been quenching the blaze daily.

“The owner is doing their best to try to extinguish it,” she said.

Contra Costa County Health Services tweeted Sunday that the agency was “monitoring air quality in Bay Point/Pittsburg where the former Marsh Fire is smoldering.”

“Air quality at this time is in the acceptable range,” officials said. “We continue to monitor and will advise the community if conditions change.”

Air quality levels in Pittsburg and the East Bay were in the “good” and “moderate” levels on Sunday, according to The Chronicle’s air quality tracker.

Kristine Roselius, a spokeswoman for the Bay Area Air Quality Management District, confirmed in a statement Sunday that air quality levels were “not currently unhealthy, but we are experiencing higher than normal levels of fine particulates.”

That’s due to a temperature inversion, she said, which happens when the air closest to the ground is cooler than higher elevations, trapping fine particles from car exhaust and fireplaces at the ground level.

“But air quality levels will improve when the weather pattern changes in the next few days,” Roselius said.

Jessica Flores is a San Francisco Chronicle staff writer. Email: jessica.flores@sfchronicle.com Twitter: @jesssmflores

Jessica Flores is a reporter for The San Francisco Chronicle. Before joining The Chronicle in 2021, she worked for USA Today, NPR affiliate KPCC and Curbed LA. Originally from L.A., she received her master's degree in journalism from the University of Southern California and a bachelor's degree from Mount Saint Mary's University in Los Angeles.