About 3 million gallons of untreated sewage spilled into Puget Sound on Friday after backup pumping systems failed.

The North and South beaches at Seattle's Discovery Park are reopen after a sewage spill investigation. The beaches reopened Monday afternoon after three days of water quality testing.

Three Kitsap County beaches also reopened Monday after millions of gallons of untreated sewage poured into Puget Sound last week.

Fay Bainbridge Park, Indianola Dock, and Joel Pritchard Park closed Friday after models from the Washington Department of Health showed that the King County sewage spill could reach those areas, according to the Washington State Department of Ecology.

The Washington State Department of Ecology blamed the spill on pumping system failures at two of King County's largest sewage treatment plants: the West Point Wastewater Treatment Plant and the Renton Wastewater Treatment Plant.

The system failures were likely caused by power disruptions at the plant.

The West Point Wastewater Treatment Plant released an estimated 3 million gallons of untreated sewage for about 27 minutes after backup pumping systems failed, according to Ecology. A spokesperson for the King County Wastewater Division told KING 5 on Saturday that 80% of the spill was stormwater.

"We really need to look at the power supplies that are coming into our treatment plan and work with our power providers and make sure the quality of the power, and the reliability of that power, is there as well," said Christie True, director of King County Natural Resources and Parks.

On July 18, there was a separate power failure at King County’s Renton Wastewater Treatment Plant resulting in “potentially limited disinfection of treated wastewater.” The limited disinfection lasted about 50 minutes. The plant discharges into Puget Sound about two miles northwest of Duwamish Head in Seattle.

Ecology is investigating both incidents as discharges that would violate the state's water quality permits for the facilities.