Fire's Threat To Bay Area's Water Supply May Come Later : The Two-Way The huge "Rim Fire" in and around Yosemite National Park is close to the Hetch Hetchy Reservoir that serves San Francisco. While falling ash hasn't seriously polluted the waters yet, there's concern that erosion from scorched hillsides will cause problems for the water supply in coming months.

Fire's Threat To Bay Area's Water Supply May Come Later

A charred caution sign just outside of California's Yosemite National Park. David McNew /Reuters/Landov hide caption

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David McNew /Reuters/Landov

A charred caution sign just outside of California's Yosemite National Park.

David McNew /Reuters/Landov

The huge "Rim Fire" in and around California's Yosemite National Park hasn't yet caused problems at the Hetch Hetchy Reservoir that provides water to 2.6 million people in the Bay Area. There have been fears that falling ash will pollute the water there.

But now, the San Francisco Chronicle reports, "wildfire experts say problems for San Francisco's water agency may come later. Hetch Hetchy's pristine waters will be vulnerable to eroding hillsides as the fire leaves behind torched soil that can't absorb autumn rains and leveled forests that no longer anchor steep mountain slopes."

There's also word from KQED Wednesday morning that the flames are "perilously close to a longstanding experimental forest near Sonora. Losing it would be a setback for forestry and as fate would have it, fire management. For 80 years, the Stanislaus-Tuolumne Experimental Forest has been a trove of data for foresters."

Southern California Public Radio, which has been updating an online "Fire Tracker" with data about blazes in the state, continues to add information about the Rim Fire here. As of 7:45 a.m. ET Wednesday, it was reporting that the fire was 20 percent contained and had burned 184,481 acres.

KQED, meanwhile, has posted a graphic produced by the federal government's InciWeb that offers a colorful look at the Rim Fire's growth since the blaze broke out on Aug. 17.

In case you missed it, this post we published on Tuesday is still worth checking out: "STUNNING VIDEO: Pilots' View Of California's Rim Fire."