Kauai County officials said they anticipate Kalapaki Beach will remain closed until at least Friday afternoon because of a sewage spill Wednesday night at the Lihue Wastewater Treatment Plant.

An estimated 400,000 to 500,000 gallons of partially treated sewage flowed from the plant, situated above Kauai Lagoons Golf Course, into the storm drain system that leads into Kalapaki Bay, officials said.

Officials said the spill resulted from a partial power outage involving a circuit within the facility about 5 p.m. The sewage that spilled had completed secondary treatment but not tertiary treatment.

Public Works officials closed the beach and crews took water samples to determine water quality. Signs warning of the spill were posted along the beach.

“Our main focus at this point is public health and safety,” County Engineer Larry Dill said. “We understand and apologize for the inconvenience to our residents, visitors and surrounding business and we are working diligently to get the beach reopened as soon as it is prudent to do so.”