City workers still don’t know what caused a 20-inch sewer pipe to crack Thursday morning, sending hundreds of thousands of gallons of raw sewage directly through one man’s yard and into North Creek.

Crews got the pipe replaced at 7 a.m. Friday.

The city is warning people to avoid contact with North Creek. Signs have been posted in some areas along the Creek asking people to avoid contact.

The results of water quality samples taken from North Creek aren’t available yet but the expectation is that there will be high levels of bacteria present, said city spokeswoman Kate Reardon.

Crews worked through the night to replace the cracked pipe, located at 11800 block of Silver Way, said The break occurred around 6 a.m. yesterday. Crews used heavy equipment and sand bags to divert as much of the flow as possible.

The damage was worse than originally thought. Workers had to replace a 25-foot section of pipe. The damage to the creek and to one man’s basement and yard is still being tallied. Reardon called it “a significant event.”

The pipe that cracked was installed in the late 1980s. That’s not old for pipes, which can last 80 years or longer, she said.

The city plans to make right the homeowner’s yard and basement that were flooded with sewage, she said.

City workers were in contact throughout the event with multiple organizations and agencies such as the state departments of Ecology and Fish &Wildlife, the Snohomish Health Department, Snohomish County, nearby cities, nearby school districts, Alderwood Water &Sewer District, Tulalip Tribes and the Muckleshoot Indian Tribe Fisheries Division.

The Alderwood Water &Sewer District had crews working at various points in its system as well to reduce sewage flows to the break point.

The event did not affect drinking water.