Rim Fire Near Yosemite Grows Slightly, 80 Percent Contained

The Rim Fire burning on the outskirts and inside Yosemite National Park reached 80 percent containment on Wednesday morning, the 18th day of the blaze, despite the fact that it grew by about 1,500 acres.

Cal Fire spokesman Dave Berlant said the fire has now charred 237,341 acres, up from 235,841, or 368 square miles, the day before. A total of 4,100 firefighters are still surrounding the Stanislaus National Forest, where the fire started on Aug. 17.

Firefighters don't expect the fire to be fully contained until Sept. 20.

Even though all mandatory and voluntary evacuations have been lifted, more than 5,500 structures remain threatened. Highway 120 at the Yosemite National Park boundary west to Buck Meadows also remains closed.

There has been some speculation about the cause of the fire, including from one Twain Harte fire chief who says he suspects it may have started at an illegal marijuana grow camp at the Jawbone Ridge. But the U.S. Forest Service, which is the lead agency on the Rim Fire, has not offered an official determination on what sparked what has become the fourth largest wild fire in California history.

On Wednesday, Tuolumne County Sheriff Sgt. Scott Johnson told NBC Bay Area that his county is among the "top five" in California for illegal marijuana grow sites, and that teams have uncovered "a lot" of pot camps over the years near where the fire broke out.

Still, Johnson said it's "irresponsible" to speculate on what started the fire at this point. He suspects the fire chief's theory has attracted widespread attention thanks to his comments being captured on an Aug. 23 YouTube video of a community meeting, where he says illegal marijuana growers likely could have started the fire. The sheriff said he's been asked about the marijuana speculations from various news agencies, including the Mercury News, which first reported the story, CNN, CSNBC, Reuters, Canadian Broadcasting and "someone in France."

Todd McNeal, the chief, has not returned several calls by NBC Bay Area seeking comment about his remarks. On Wednesday, the National Interagency Fire Center confirmed there were no lightning strikes in the area of the fire when it broke out, ruling out that possibility.

MORE: Hetch Hetchy Reservoir Water Remains Safe for Drinking

Some public health and safety risks related to the Rim Fire have died down over the last 10 days or so. On Tuesday, San Francisco officials announced that the Hetch Hetchy Reservoir, located in Tuolumne County, is safe to drink despite being so close to the fire. The system provides drinking water to 2.5 million customers.

Two of three hydroelectric powerhouses that supply the Hetch Hetchy system - the Kirkwood and Holm turbines - were taken offline on Aug. 19 because they suffered some fire damage. But on Tuesday, the Kirkwood facility resumed activity, providing power after repairs were made over the weekend, according to San Francisco Public Utility Commission officials.

Holm is San Francisco's largest powerhouse and crews are still working to get it back online. But utility officials said at a news conference on Tuesday that the power supplies have never been disrupted because the Moccasin Powerhouse in Tuolumne County has been generating power throughout the blaze. Since the shutdowns,San Francisco has spent about $860,000 on buying alternative energy sources.