Yosemite’s Rim Fire: reservoir threatened, but firefighters ‘making progress’

The wildfire in and around California’s Yosemite National Park has spread to more than 280 square miles of land and is raining ash on a reservoir that supplies water and hydro-electric power to San Francisco.

More from GlobalPost: Wildfire near Yosemite threatens San Francisco's power supply; giant sequoias

The Hetch Hetchy reservoir, located inside Yosemite, provides water for 2.6 million people in the San Francisco Bay area.

To protect the water supply, city officials said they are moving water from the Hetch Hetchy to reservoirs closer to San Francisco.

"We're taking advantage that the water we're receiving is still of good quality," Harlan Kelly Jr., general manager of the San Francisco’s Public Utilities Commission, told USA Today. "We're bringing down as much water as possible and replenishing all of the local reservoirs."

If the fire does contaminate the Hetch Hetchy, utility officials said they have a six-month supply of water in reservoirs near the Bay area.

The fire is now the largest active wildfire in the United States and the 11th-largest in California’s recorded history.

While the fire remains ferocious, officials said the work of the 3,700 firefighters battling the blaze – including digging dirt lines and dropping water and retardant from helicopters – was beginning to pay off.

As of Tuesday, the fire was 20 percent contained.

"Slowly but surely, we are making progress," Cal Fire spokesman Daniel Berlant told the San Jose Mercury News.

The cost of fighting the fire has climbed to more than $20 million.