About 123,000 gallons of untreated wastewater spilled into a Havelock waterway on Thursday.
Officials said the spill was caused by rainwater from Tropical Storm Idalia flooding the sewer system.
It happened on Pineview Street near Webb Blvd, and the untreated water made its way to Joe's Branch, an offshoot of Slocum Creek.
Slocum Creek has failed the Swim Guide test 11 out of 13 times since Memorial Day.
The NCDEQ Division of Water Resources is investigating.