The massive Rim Fire, which began Aug. 17, on Monday was nearing the Hetch Hetchy Reservoir, threatening San Francisco and a big chunk of the East Bay Area’s power and water supplies.

A state of emergency for San Francisco is in place on Gov. Jerry Brown’s orders as the Rim Fire edged its way across the spectacular Sierra Nevada Mountains and into the Yosemite National Forest, threatening the city’s power and water supplies.

Hetch Hetchy Reservoir, 160 miles east of San Francisco and 3,000 feet above sea level, supplies 85% of the water and powers the wide-ranging transit system, as well as San Francisco International Airport and San Francisco General Hospital.

Hetchy’s water flows through tunnels to serve more than 2.6 million water customers in San Francisco and across the Bay Area. The system is linked to the East Bay Municipal Utilities District serving Oakland and nearby communities, as well as the Santa Clara Valley Water District, according to the San Francisco Public Utilities Commission.

The commission has deactivated transmission lines near the fire and as of Monday it already had spent close to $600,000 on the open market to buy power supplies.

Commission spokesman Tyrone Jue said the fire had yet to cause a “change or impact” to the city’s “water quality or delivery” from the reservoir.

Brown’s emergency declaration cited “conditions of extreme peril.” The state already has secured federal financial assistance to combat the blaze, according to the California Emergency Management Agency.

On Monday afternoon state officials said about 15% of the blaze had been contained but not before it had charred close to 234 square miles, or close to 200,000 acres, as it blazed its way through parts of Northern California. Close to 3,000 emergency personnel from California and other states were battling the Rim Fire, which erupted on Aug. 17 in Stanislaus National Forest.

Forest fires this summer have damaged other utility systems in Southern California, according to the California Independent System Operator, which manages the state’s power grid. It said a fire north of Los Angeles in June created “multiple forced outages” on transmission lines that connect to Northern California and the Pacific Northwest.