According to Cal Fire, the Rim Fire -- which started on Aug. 17 -- has burned more than 133,000 acres in Stanislaus National Forest and was only 7 percent contained as of this morning.
The Rim Fire has become California's 15th largest blaze in the state's recorded history, Cal Fire said.
The fire has threatened more than 4,500 homes and approached the Hecty Hetchy Reservoir and watershed, which supplies water and hydroelectric power to over 2.6 million Bay Area residents.
The San Francisco Public Utilities Commission issued a statement today reassuring its customers that water quality and utility service have not been impacted, even though the agency was forced to shut down power lines due to fire damage at a hydroelectric facility last week.
"All of San Francisco's municipal customers continue to be fully supplied; there will be no interruption in electric service," the SFPUC statement said.
Repair crews were set to return to the Kirkwood Powerhouse today to make preliminary repairs and damage assessments.
Since Aug. 19, the SFPUC has spent an estimated $600,000 to purchase electricity from other sources while the transmission lines from Tuolumne County are shut down.
So far the blaze has not reached Hetch Hetchy Reservoir or caused any damage to O'Shaugnessy Dam, according to the SFPUC.
The water quality was being continually tested to ensure that fallout from the fire has not jeopardized the water supply downstream. The water quality remains high and the supply is safe, according to the SFPUC.
Gov. Jerry Brown declared a state of emergency for the City and County San Francisco on Friday due to the effects of the Rim Fire on the city's property and power and water infrastructure.
In addition, Brown secured a grant from the Federal Emergency Management Agency that will reimburse around 75 percent state and local firefighting expenses, according to the California Emergency Management Agency.
The cause of the fire has not been determined.