King County says that testing indicates water quality has returned to normal in Lake Ballinger after a March 14 sewer backup caused approximately 236,000 gallons of sewage overflow into the lake and onto nearby properties.

The lake, which has been closed for recreational use since late last week, is now open.

The cause of the wastewater backup at the Lake Ballinger Pump Station, which affected the 30-inch Edmonds sewer line along the south side of Lake Ballinger, is under investigation, said King County Wastewater Division spokesman Norm Mah. The backup caused sewage to overflow along approximately 12 properties, he said.

City of Edmonds Public Works Director Phil Williams said that most of the Edmonds residents who live along the lake have built a berm between their backyards and the lake to alleviate flooding that brings lake water into their properties. As a result, most of the sewage from those properties “ponded up behind the berm so it didn’t go into the lake,” Williams said.

The cleanup has been completed at those properties and landscape restoration is underway, Mah said. In addition, four side sewers that were affected have been repaired.

“The water quality sampling results over the weekend showed water quality has returned to normal and four notification signs have been removed that were placed at the Lake Ballinger Park and Nile Shriners Golf Course,” Mah said.

Lake Ballinger sits between the cities of Mountlake Terrace and Edmonds.

The Lake Ballinger Pump Station is located at 2205 N. 205th St. in Shoreline, on the King/Snohomish County border. Sewage flows out of the pump station are part of a “flow swap arrangement” with King County and the City of Edmonds, which also treats sewage from the City of Mountlake Terrace. Under that arrangement, Edmonds treats wastewater from Richmond Beach in exchange for an equal amount of Lake Ballinger area flow that is sent to the King County treatment system.