Untraeted sewage could flow into Lake Illawarra under a Sydney Water proposal to manage sewer overflows in Berkeley.It is proposed that during heavy rain, stormwater and untreated sewage would be diverted into a stormwater channel that empties into Hooka Creek, only about 1km upstream from where the creek flows into Lake Illawarra.Residents near Fred Finch Park have been notified by Sydney Water that it is considering constructing an "emergency relief structure" to reduce the frequency of sewage overflowing into private properties and residential backyards when the sewerage system backs up during extreme weather. The overflows have been linked to a maintenance hole on Hooka Creek Rd."The overflows will be considerably diluted with stormwater and will be further diluted by the flows in the creek," a Sydney Water fact sheet said."The environmental impacts will therefore be minor, especially compared to the public health benefits of diverting overflows from private properties."The Berkeley side of Lake Illawarra is popular for fishing, kayaking and boating, and resident Alice Scott was concerned."They have finally got the lake fixed up, the prawns and the fish are back, and it is much cleaner and healthier," she said."But we don't know what might flow in there if they go ahead with this plan."She was worried about unknown quantities of E coli bacteria entering the lake."Never mind a stopgap - we want this stormwater issue fixed properly," Ms Scott said."What guarantee do we have that the same thing won't happen in Windang, Mt Warrigal or Oak Flats? We don't want our lake to become a cesspool."Sydney Water met residents on Saturday and has also met Wollongong City Council."Sydney Water will complete further investigations and is aiming to come back to the community with more options by the end of October," a Sydney Water spokesman said yesterday.Lake Illawarra Authority chairman Doug Prosser said if the alternative was sewage backing up into people's homes, he could see little option."Since we put in the new entrance, the water quality is surprisingly good considering we have 190 drains, 15 creeks and 20 sewage overflows that go into the lake," he said."We have to be pragmatic, and it is better than it used to be when the old Berkeley pumping station used to overflow regularly."Sydney Water claims it already has 120 emergency relief structures in place across the Illawarra, diverting sewage and stormwater overflows into waterways."Sydney Water is committed to reducing overflows from its sewerage systems through the $560 million SewerFix program," the spokesman said.