San Francisco's aging seawall is in need of repairs.
The Port of San Francisco said preliminary findings of an earthquake study show the mud holding the wall in place is weak.
"It holds back the bay," said Elain Forbes, Port of San Francisco's interim director. "Literally holds back the bay from portions of the city."
The 100-year-old seawall stretches three and a half miles long and protects 700 acres of the city, including expensive real estate, critical infrastructure and transportation.
"The issue is the seawall moving and infrastructure around it moving," Forbes said.
Seawall movement could mean disaster for a large portion of the city and snarl emergency plans. The seawall could give in a large earthquake, which would devastate San Francisco's iconic waterfront.
Ferries are expected to be used for evacuations and emergency supply delivery.
"Really what we're looking at is improving the condition of mud around the seawall and strengthening it so the sea wall stays in place," Forbes.
Strengthening the seawall is expected to cost billions of dollars.
Final results of a seawall earthquake study are expected next month. The Port of San Francisco said before it decides on how to fix the wall, it will also have to factor in sea level rise.