SACRAMENTO, Calif. -- Scientists are assessing the damage from a massive wildfire burning around Yosemite National Park, laying plans to protect habitat and waterways as the fall rainy season approaches.

Members of the federal Burned Area Emergency Response team were hiking the rugged Sierra Nevada terrain Saturday even as thousands of firefighters still were battling the four-week-old blaze, now the third-largest wildfire in modern California history.

Federal officials have amassed a team of 50 scientists, more than twice what is usually deployed to assess wildfire damage. With so many people assigned to the job, they hope to have a preliminary report ready in two weeks so remediation can start before the first storms, Alex Janicki, the Stanislaus National Forest BAER response coordinator, said.

Team members are working to identify areas at the highest risk for erosion into streams, the Tuolumne River and the Hetch Hetchy Reservoir, San Francisco's famously pure water supply.

The wildfire started in the Stanislaus National Forest on Aug. 17 when a hunter's illegal fire swept out of control and has burned 394 square miles of timber, meadows and sensitive wildlife habitat.

It has cost more than $89 million to fight, and officials say it will cost tens of millions of dollars more to repair the environmental damage alone.

About 5 square miles of the burned area is in the watershed of the municipal reservoir serving 2.8 million people - the only one in a national park.

"That's 5 square miles of watershed with very steep slopes," Janicki said "We are going to need some engineering to protect them."

So far the water remains clear despite falling ash, and the city water utility has a six month supply in reservoirs closer to the Bay Area.

The BAER team will be made up of hydrologists, botanists, archeologists, biologists, geologists and soil scientists from the U.S. Forest Service, Yosemite National Park, the Natural Resource Conservation and the U.S. Geological Survey.

The team also will look at potential for erosion and mudslides across the burn area, assess what's in the path and determine what most needs protecting.

"We're looking to evaluate what the potential is for flooding across the burned area," said Alan Gallegos, a team member and geologist with the Sierra National Forest. "We evaluate the potential for hazard and look at what's at risk -- life, property, cultural resources, species habitat. Then we come up with a list of treatments."

In key areas with a high potential for erosion ecologists can dig ditches to divert water, plant native trees and grasses, and spray costly hydro-mulch across steep canyon walls in the most critical places.

Fire officials still have not released the name of the hunter responsible for starting the blaze. On Friday Kent Delbon, the lead investigator, would not characterize what kind of fire the hunter had set or how they had identified the suspect.

"I can say some really good detective work out there made this thing happen," he told the Associated Press.

Delbon said the Forest Service announced the cause of the fire before being able to release details in order to end rumors started by a local fire chief that the blaze ignited in an illegal marijuana garden.

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  • Firefighters enter a grove of giant sequoias in Yosemite National Park in this photo made on Sunday, Aug. 25, 2013, and released by the National Park Service on Tuesday. (AP Photo/National Park Service)

  • AP10ThingsToSee - Inmate firefighters walk along state Highway 120 as firefighters continue to battle the Rim Fire near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong, File)

  • The Rim Fire burns through trees near Yosemite National Park, Calif., on Tuesday, Aug. 27, 2013. (AP Photo/Jae C. Hong)

  • Russell Mitchell

    Firefighter Russell Mitchell, left, monitors a back burn during the Rim Fire near Yosemite National Park, Calif., on Tuesday, Aug. 27, 2013. (AP Photo/Jae C. Hong)

  • The Rim Fire burns through trees near Yosemite National Park, Calif., on Tuesday, Aug. 27, 2013. (AP Photo/Jae C. Hong)

  • A videographer records the Rim Fire burning through trees near Yosemite National Park, Calif., on Tuesday, Aug. 27, 2013. (AP Photo/Jae C. Hong)

  • A smoke plume from the Rim Fire rises nera Yosemite National Park, Calif., on Monday, Aug. 26, 2013. (AP Photo/Jae C. Hong)

  • A helicopter reloads fire retardant as firefighters continue to battle the Rim Fire in Tuolumne City, Calif., on Monday, Aug. 26, 2013. (AP Photo/Jae C. Hong)

  • Aerial Water Drop on Rim Fire

    In this Thursday, Aug. 22, 2013 photo provided by the California Army National Guard on Monday, Aug. 26, 2013, Sgt. Chris Boni, crew chief from the 1-140th Aviation Battalion (Air Assault) from Los Alamitos Joint Training Base (JFTB), releases water to help control the Rim fire below near Yosemite National Park, Calif. The The UH-60 Black Hawk Crews are battling the Rim wildfire, one of the largest in California history, in support of the U.S. Forest Service and CAL FIRE. (AP Photo/U.S. California Air National Guard, Master Sgt. Julie Avey)

  • In this Thursday, Aug. 22, 2013 photo provided by the California Army National Guard on Monday, Aug. 26, 2013, Sgt. Chris Boni, crew chief from the 1-140th Aviation Battalion (Air Assault) from Los Alamitos Joint Training Base (JFTB), releases water to help control the Rim fire below near Yosemite National Park, Calif. The The UH-60 Black Hawk Crews are battling the Rim wildfire, one of the largest in California history, in support of the U.S. Forest Service and CAL FIRE. (AP Photo/U.S. California Air National Guard, Master Sgt. Julie Avey)

  • Smoke clouds and bands of haze from the Rim Fire in the western Sierra Nevada loom up some 20 miles behind the famed granite monolith known as Half Dome, right center, seen from 11,500-foot Mt. Clark in Yosemite Valley in Yosemite National Park, Calif., Saturday, Aug. 24, 2013. (AP Photo/Tami Abdollah)

  • A fire truck drives past burning trees as firefighters continue to battle the Rim Fire near Yosemite National Park, Calif., on Monday, Aug. 26, 2013. (AP Photo/Jae C. Hong)

  • A burned SUV sits in front of a campground destroyed by the Rim Fire near Yosemite National Park, Calif., on Monday, Aug. 26, 2013. (AP Photo/Jae C. Hong)

  • A helicopter drops water over a hot spot while battling the Rim Fire near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong)

  • A.J. Tevis

    Firefighter A.J. Tevis watches the flames of the Rim Fire near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong)

  • The Rim Fire burns along Highway 120 near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong)

  • The Rim Fire burns along Highway 120 near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong)

  • A smoke rises from smoldering trees as firefighters continue to battle the Rim Fire near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong)

  • Firefighter Charlie Ferris, of Los Angeles, watches a smoke plume from the Rim Fire near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong)

  • A firefighter watches for spot fires during a burnout operation while battling the Rim Fire near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong)

  • Inmate firefighters walk along Highway 120 after a burnout operation as firefighters continue to battle the Rim Fire near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. (AP Photo/Jae C. Hong)

  • The smoke generated by the Rim Fire rises under a star-filled sky near Yosemite National Park, Calif., on Sunday, Aug. 25, 2013. Fire crews are clearing brush and setting sprinklers to protect two groves of giant sequoias as a massive week-old wildfire rages along the remote northwest edge of Yosemite National Park. (AP Photo/Jae C. Hong)

  • GROVELAND, CA - AUGUST 28: Cows graze in a field as the Rim Fire burns in nearby hills on August 28, 2013 near Groveland, California. Over 3,500 firefighters are battling the destructive Rim Fire that has charred 180,000 acres and has entered a section of Yosemite National Park. The fire is currently 23 percent contained. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 28: A CalTrans worker takes a break during a tree cutting operation in an area that was burned by the Rim Fire during a media tour of the fire area on August 28, 2013 near Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 25: A burned car sits on the side of the road after being consumed by the Rim Fire on August 25, 2013 near Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • YOSEMITE NATIONAL PARK, CA - AUGUST 25: Trees burned by the Rim Fire stand on August 25, 2013 in Yosemite National Park, California. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 25: Flames from the Rim Fire consume trees on August 25, 2013 near Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 25: U.S. Fish and Wildlife Service firefighter Corey Adams sits on a tree stump as he monitors the Rim Fire on August 25, 2013 near Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 24: West Stanislaus County Fire firefighters monitor the Rim Fire along highway 120 on August 24, 2013 near Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 24: A firefighter uses a hose to douse the flames of the Rim Fire on August 24, 2013 near Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • YOSEMITE NATIONAL PARK, CA - AUGUST 24: Smoke from the Rim Fire lingers over the O'Shaughnessy Dam at Hetch Hetchy Reservoir on August 24, 2013 in Yosemite National Park, California. (Photo by Justin Sullivan/Getty Images)

  • YOSEMITE NATIONAL PARK, CA - AUGUST 24: U.S. Forest Service firefighter Chris Brossard monitors a spot fire while battling the Rim Fire on August 24, 2013 in Yosemite National Park, California. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 25: Flames from the Rim Fire consume trees on August 25, 2013 near Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • YOSEMITE NATIONAL PARK, CA - AUGUST 24: A firefighter uses a hose to douse a spot fire while battling the Rim Fire on August 24, 2013 in Yosemite National Park, California. (Photo by Justin Sullivan/Getty Images)

  • In this undated photo provided by the U.S. Forest Service, the Rim Fire burns near Yosemite National Park, Calif. (AP Photo/U.S. Forest Service)

  • GROVELAND, CA - AUGUST 22: A firefighter from Central Calaveras Fire monitors the Rim Fire on August 22, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • YOSEMITE NATIONAL PARK, CA - AUGUST 22: Smoke from the Rim Fire is visible near the Hetch Hetchy reservoir on August 22, 2013 in Yosemite National Park, California. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 22: A firefighting helicopter flies in front of a plume of smoke from the Rim Fire on August 22, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • In this undated photo provided by the U.S. Forest Service, the Rim Fire burns near Groveland Ranger Station in Groveland, Calif. (AP Photo/U.S. Forest Service)

  • GROVELAND, CA - AUGUST 22: Firefighters from the Colorado based South Arkansas Fire District monitor the Rim Fire on August 22, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 22: Firefighters monitor a plume of smoke from the Rim Fire on August 22, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 22: A U.S. Forest Service firefighter monitors a radio while battling the Rim Fire on August 22, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 22: A firefighter from the Kern County Rio Bravo Hotshots looks for flying embers while battling the Rim Fire on August 22, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 22: Firefighters douse hot spots while battling the Rim Fire on August 22, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 21: Firefighters from Ebbetts Pass Fire District monitor a back fire as they battle the Rim Fire on August 21, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 21: A firefighter from Ebbetts Pass Fire District uses a drip torch to light a back fire as they battle the Rim Fire on August 21, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 21: Firefighters from Ebbetts Pass Fire District monitor a back fire as they battle the Rim Fire on August 21, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 21: A firefighter from Ebbetts Pass Fire District monitors a back fire as he battles the Rim Fire on August 21, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 21: Firefighters from Ebbetts Pass Fire District monitor a back fire as they battle the Rim Fire on August 21, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • GROVELAND, CA - AUGUST 21: A firefighter from Ebbetts Pass Fire District uses a drip torch to light a back fire while battling the Rim Fire on August 21, 2013 in Groveland, California. (Photo by Justin Sullivan/Getty Images)

  • BUCK MEADOWS, CA - AUGUST 21: Fire consumes trees along US highway 120 as the Rim Fire burns out of control on August 21, 2013 in Buck Meadows, California. (Photo by Justin Sullivan/Getty Images)