SAN FRANCISCO, Calif. (KGO) --Access to San Francisco's main water supply is being shut down for 60 days to inspect a nearly 100-year-old tunnel.
Hidden in the Sierra Nevada is an 18 mile long mountain tunnel that streams water into the Bay Area.
"Just walking through a mountain and the walls are granite, that's what the unlined portion looks," said Charles Sheehan of the San Francisco Public Utilities Commission. "So if you think of driving through a tunnel it looks more like that."
Sheehan says the nearly 100-year-old Hetch Hetchy system shows some wear. "In our last inspection we noted that there was some deterioration of the lining of the tunnel," he told ABC7 News.
Officials are cutting off the Hetch Hetchy flow to inspect the tunnel Tuesday. The 60 day shut down is twice as long as usual inspections.
Five regional reservoirs are already in service and have been for a few weeks. The 2.6 million people served by Hetch Hetchy shouldn't notice a difference at the tap. This inspection is different. It determines the fate of the mountain tunnel.
The shutdown ends in early March then the SFPUC will make a decision in the coming months.