The epic Rim Fire is not only threatening large swaths of wild forest and communities near Yosemite National Park, but the San Francisco Public Utilities Commission water and power system.
The Hetch Hetchy Reservoir is located in the national park where the fire had spread as of this morning.
The fire has charred more than 125,000 acres, destroyed 16 structures and was only 5 percent contained since it started Saturday in the Stanislaus National Forest, according to the U.S. Fire Service.
SFPUC deputy general manager Michael Carlin said this morning the fire has had no affect on water quality or supply for the 2.6 million customers in the Bay Area.
Water is drawn from 270 feet below the surface of Hetch Hetchy and sent through a dam and tunnels that send it toward the Bay Area.
"We don't see any degradation at this time," he said. "But we are monitoring the situation."
The water is at a safe clarity, he said, and although ash on the water is a concern, it has not presented any issues thus far, he said.
The fire is moving toward the reservoir, which has prompted the utility commission to enact contingency plans to ensure seamless delivery of water to local residents and businesses, Carlin said.
According to SFPUC water operations manager David Briggs, local sources of water from the Santa Clara Valley Water District and East Bay Municipal Utilities District are prepared for use and there are enough supplies for several months.
The decision to switch to local reserves would depend on the turbidity, or cloudiness, of the water at the Yosemite reservoir. Currently monitors indicate the water is at its normal .2 NTUs, which is a measure of cloudiness, Briggs said.
If the water makes it up to 5.0 NTUs, which is a state-mandated water quality standard, contingency plans would move forward, Briggs said.
In that case, water demands would still be met with no discernable changes to service, he said.
Carlin said the utilities commission has declared an emergency situation, but thus far the water system has not been affected.
There has been limited opportunity to evaluate any damage to facilities and all water department crews have been evacuated from the area, he said.
Because of the blaze, part of the utilities' power system has been taken offline. Only one of three powerhouses that use water to create hydroelectricity is in use.
Enough power is still being generated and the utility is working with PG&E to ensure enough supplies, Carlin said.
More than 12 miles of power lines have been damaged in the fire and other damages are possible but unknown at this point, Carlin said.
The cause of the fire is under investigation. More than 2,000 firefighters have responded to the expanding blaze, according to the forest service.