Hawaii American Water said 1 million gallons of "treated un-disinfected" sewage made its way into the ocean after an underground electrical line failed on Tuesday.
The company’s East Honolulu Wastewater Treatment Plant serves the Hawaii Kai area and is located across from Sandy Beach.
"We regret this incident and are working to replace the power line that failed yesterday,” said Hawaii American Water Manager Lee Mansfield.
The sewage "had gone through normal processing, including biological treatment, but was not disinfected with chlorine before discharge to our ocean outfall," the company said in a news release about 6 p.m. Wednesday.
The company said there was no health risk for anyone who swam in affected waters "because the wastewater had been treated and our outfall discharges a quarter of a mile off-shore at a depth of approximately 40 feet."
Signs are being posted at Sandy Beach, and daily water testing is planned.