National park wildfire rains ash on San Francisco’s water supply

Utility bosses scrambled to send more water towards the metropolitan area before it became tainted as nearly 3,700 firefighters battled the 230sq mile blaze, the biggest wildfire on record in California’s Sierra Nevada.

They reported modest progress, saying the fire was 15 per cent contained.

Experts monitored the Hetch Hetchy Reservoir for clarity and used a massive new £3bn gravity-operated pipeline system to move water quickly to reservoirs closer to San Francisco. The Hetch Hetchy supplies water to 2.6 million people in the Bay area, 150 miles away.

“We’re taking advantage that the water we’re receiving is still of good quality,” said Harlan Kelly, general manager of the city’s Public Utilities Commission. “We’re bringing down as much water as possible and replenishing all of the local reservoirs.”

At the same time, officials gave assurances that they had a six-month supply of water in reservoirs near the Bay area.

So far the ash that has been raining on to the Hetch Hetchy has not sunk as far as the intake valves, which are about halfway down the 300ft O’Shaughnessy Dam. Utility officials said that the ash is non-toxic but that the city will begin filtering water for customers if problems are detected. That could cost more.

Power generation at the reservoir was shut down last week so that firefighters would not be imperiled by live wires. San Francisco is buying replacement power from other sources to run City Hall and other municipal buildings.

It has been at least 17 years since fire ravaged the northernmost stretch of Yosemite that is under siege.

Park chiefs cleared brush and set sprinklers on two groves of giant sequoias that were seven to 10 miles away from the fire’s front lines.

The blaze began on August 17.