King County is working to stop erosion along a portion of Coal Creek that is creating the potential for sewage to be discharged into the water that runs into Lake Washington.

Heavy precipitation has caused the erosion of loose soils in the creek bank, diverting its flow toward a sewer pipe and manhole that King County worries will be exposed this winter. If the pipe is damaged, sewage would flow from Coal Creek — through the Newport Shores neighborhood — into Lake Washington.

“October was the worst month for it,” said Cindy Clark, King County water quality planner and project manager. “Something really changed there and the stream migrated toward the infrastructure.”

King County is awaiting state and federal approval to construct stream enhancements 200 feet from an existing control structure at Interstate 405 and extending upstream for 700 feet. Clark said the hope is to begin construction in August, the project having to be done by Sept. 30, when fish migration prohibits work in Coal Creek. The project is expected to take three weeks to complete, she said.

A portion of the channel will be excavated to force the stream away from the erosion, the project site located southeast of the intersection of Coal Creek Parkway and 119th Avenue Southeast.

Long logs also will be spaced along Coal Creek, some partially buried into the bank. Rock and other materials will also be used for anchoring. Clark said because a large pool near the manhole will need to be filled, smaller pools will be constructed inside the stream.