A dredging company this week sheared a sewage line, spilling thousands of gallons of bacteria-filled matter into Newport Bay.
The area will be closed to swimmers through at least the weekend.
Orange County Health Care Agency officials said they will need to see two consecutive days of clean samples from the water off the east edge of Newport Harbor, from Bayside Drive at Balboa Island to the edge of the Harbor Patrol headquarters to the south, before they reopen it.
In the meantime, city workers and crews from RE Staite, the dredging company that broke the line, will investigate the break and figure out how to fix it.
About 11 p.m. Wednesday, a dredging vessel broke off a 3-foot piece of an 8-inch wide main sewer line between the island and the mainland at Bayside Drive, spilling about 2,800 gallons of raw sewage into the water.
It took city crews nearly three hours to stop the spill, said Harbor Resources Manager Chris Miller.
When crews tried to divert the sewage to the city's backup line, they hit another problem. That line was installed in the 1930s, and one of its valves failed to close all the way, Miller said.
The city was forced to shut down Balboa Island's sewer system for most of Thursday and didn't start it up again until Friday afternoon, thanks to the help of nearby agencies that came to the rescue.
Vactor trucks from the county, Costa Mesa, Irvine Ranch and private contractors descended onto the island, gathered up the sewage and then redeposited it into the county's main line on the other side of the break.
"I'm really appreciative of everyone's help; it was a team effort," Miller said.
Newport Beach has since replaced its faulty valve and shifted the sewage through the line, leaving only the original issue to be resolved, Miller said.
A final cost estimate of the incident — and who will pay for it — will be determined next week, he said.