The King County Wastewater Treatment Division estimates 101,000 gallons of wastewater overflowed after lightning struck next to a West Seattle pump station on Tuesday.
The pump shut off two separate times due to power interruptions caused by the lightning.
The alarm went off just after 7 p.m. Tuesday, and KWTD responded but then it happened again. Pumps were off for 11 minutes the first time and 12 minutes the next time.
A backup generator did not kick in since the lightning did not cause a full power outage.
Seattle and King County were fined by the Department of Ecology and U.S. Environmental Protection Agency in January for violating conditions of their state water quality permits that regulate sewer overflows.
Beaches between Lincoln Park and the ferry dock were also closed.