The Marsh Fire in Bay Point started on May 27, and was still burning on July 12.

A California fire has been burning in the marshland of the San Francisco Bay Area for more than 6 weeks, and a material known as peat is fueling this blaze and making it difficult to extinguish, officials said.

"It's a very stubborn fire," said Steve Hill, the public information officer for the Contra Costa County Fire Protection District. "It's a peat fire, which means that it's burning in a combination of organic materials and minerals. Peat is good for gardens but it has a little pesky problem, a worldwide problem, in that it can spontaneously combust. The fire is burning underground in a huge area and it has proven to be really hard to put out. " 

The Marsh Fire ignited in a homeless encampment that was completely consumed by flames along with 200 acres on May 28 near Suisun and Solano Avenues in Bay Point, Hill said.

Flames spread into the peat across an area that was inaccessible to firefighters and engines and Hill said the decision was made to let the fire burn itself out.

The fire activity was limited for weeks, but on Saturday winds fanned flames and and it flared up, pushing into a grassy area of neighboring Pittsburg and threatening overhead high-voltage PG&E transmission lines and decommissioned industrial sites. 

"It could have threatened homes, but fortunately we were able to stop it," Hill said. "But our residents have been suffering from smoke and the smoke has been bad since the flare up. We're no longer satisfied with just allowing it to burn out, which often happens with a peat fire."

The fire is contained and not threatening any homes, but the smoke is significant. 

The Bay Area Air Quality Management District issued an air quality advisory due to the March Fire for eastern Contra Costa County for Tuesday, Wednesday and Thursday. 

Hill said that on July 10 and 11, a helicopter dumped more than 400,000 gallons of water on the blaze—"and it has done nothing."

"Onshore winds during the day are expected to disperse smoke but as winds die down overnight localized pollution levels may rise," the district said. You can monitor your area's air quality on the federal AirNow website.

Con Fire shares resident concerns on the stubborn peat fire burning on Bay Point & Pittsburg waterfronts. We are aggressively pursuing a solution to ending the smoke. Meantime, CC Health has issued a health advisory at //cchealth.org/, which we encourage all residents to observe. pic.twitter.com/yylFbS7lDD

Hill said the fire protection district is looking at options for putting out the fire including pumping water from the Delta onto the blaze. 

"The solution could be flooding that entire area," Hill said. "The good news is that it's surrounded by water on three sides by the Delta. The bad news is there are going to be a lot of organizations that have to approve this. We can't just go out and pump millions of gallons of water on it."

Amy Graff is the news editor for SFGATE. She was born and raised in the Bay Area and got her start in news at the Daily Californian newspaper at UC Berkeley where she majored in English literature. She has been with SFGATE for more than 10 years. You can email her at agraff@sfgate.com.