A firefighting helicopter drops water on the Marsh Fire in Pittsburg, Calif., on Saturday, Jul. 9, 2022. Firefighters are seeking to flood the wetlands where the fire is burning, as other painstaking efforts to fight the blaze produced only limited results. Smoke from the fire is fouling nearby air quality.

Eager to extinguish the stubborn and smoky Marsh Fire burning in Pittsburg and Bay Point for 6½ weeks, firefighters are considering flooding the wetlands area where the blaze continues to burn in decayed vegetation.

Contra Costa County Fire Protection District authorities are working with regulatory agencies to come up with a plan to flood the area, said Steve Hill, a spokesperson for the East Bay agency.

“We are aggressively pursuing a solution that involves flooding the area,” he said, ackowledging environmental concerns and the need to win approvals from multiple regulatory agencies. “But flooding may be our only option.”

The aptly named fire is burning in a wetland area near Pittsburg and Bay Point waterfront, burning through 500 acres of peat — mossy decomposed vegetation — and brush in an area that’s difficult for firefighters to access. Because of the unstable soils, fire trucks and heavy equipment sent into the area would sink and firefighters could fall into holes in the marsh where the fire is burning beneath grass in many locations.

So far, the only way to battle the smoldering blaze has been from the skies, using helicopters from Cal Fire and Pacific Gas and Electric Co. to pour water on the fire. But even that hasn’t been very effective.

“On Monday and Tuesday, we dumped about 400,000 gallons of water — one 660-gallon bucket at a time — on the fire, and it had little to no effect,” Hill said. “That serves to show the challenge we face.”

The fire ignited May 28 in a homeless encampment near Suisun and Solano avenues in Bay Point. It swept through the encampment, injuring no one but grew to about 200 acres before firefighters stopped its forward progress.

Last Saturday, winds picked up and the fire flared, spreading into nearby Pittsburg, threatening overhead PG&E power lines and nearing decommissioned industrial plants, including a former power plant that is owned by GenOn. Firefighters from the Contra Costa County Fire Protection District, aided by Cal Fire crews dropping water from helicopters, were able to knock down the flames and stop the fire’s spread.

But the fire continues to burn in the peat, sending out clouds of smelly smoke that have prompted air quality advisories from the Bay Area Air Quality Management District and Contra Costa Health Services advising residents in Pittsburg, Antioch, Oakley and Brentwood, particularly older adults or those with asthma, lung or heart disease to keep their windows and doors closed, and minimize outdoor activity.

The air district extended its warning through Thursday and said that the clouds of smoke may dissipate during the day when offshore breezes are stronger but be worse as winds die down overnight.

Peat fires are notoriously stubborn, often burning for weeks or months before they burn themselves out — a standard strategy. But given the number of people affected by smoke from the fire, Hill said, that’s not acceptable.

So fire officials, accustomed to fighting flames, are battling bureaucracy, working with the Environmental Protection Agency, the U.S. Army Corps of Engineers, Regional Water Quality Control Board and the local mosquito abatement district, and probably others, Hill said.

While details remain to be worked out, water would likely be pumped into the area, possibly from the Delta, using existing infrastructure from an area water district or high volume pumps borrowed from another fire agency, Hill said.

“Getting regulatory approval to put out peat fires is not something we do a lot,” Hill said. “We don’t know how long it will take but we’re trying to get this done as quickly as possible. But we don’t want to create a worse problem in order to solve this problem.”

Michael Cabanatuan (he/him) is a San Francisco Chronicle staff writer. Email: mcabanatuan@sfchronicle.com Twitter: @ctuan

Michael Cabanatuan is a general assignment and breaking news reporter who's covered everything from wildfires and sports fans to protests and COVID masking requirements. He's also written extensively about transportation and covered Contra Costa County for The Chronicle. He's ridden high-speed trains in Japan, walked in the Transbay Tube, been tear-gassed in Oakland and exposed to nude protesters in the Castro. Cabanatuan worked at the Paradise Post (long before anyone heard of the town), the former West County Times (in Richmond) and the Modesto Bee before joining The Chronicle. He is a two-time graduate of UC Berkeley.