A huge fire in and around California's Yosemite National Park has continued to spread and now covers almost 600 sq km officials say.
The Rim Fire is now raining ash on a key reservoir that supplies water and hydro-electric power to San Francisco, the BBC reports.
City officials say they are moving water to lower reservoirs and monitoring supplies for contamination.
The blaze is also threatening thousands of homes and some of California's renowned giant sequoia trees.
On Monday officials said the fire was 15% contained after burning for more than a week - up from 2% containment on Friday.
Strong winds are making the fires more difficult to control.
The blaze began on 17 August in the Stanislaus National Forest but the cause is still unknown.