A failed pumping system at a construction site dumped an estimated 25,000 gallons of sewage into Olley Creek on Saturday, Aug. 15, killing fish and triggering elevated bacteria readings downstream.

The spill at 1675 Milford Church Road in Marietta is the largest single overflow in a string of sewer failures across Cobb County this year. Previous August spills ranged from 210 to 720 gallons.

Cobb County Water System staff didn't discover the damage until two days later. During routine stream monitoring on Monday, Aug. 17, crews found dead fish in Olley Creek and collected water samples, according to a CCWS press release issued Aug. 19. Lab results returned Tuesday, Aug. 18 showed elevated levels of fecal coliform and E. coli bacteria.

The overflow ran for five hours, from noon to 5 p.m. on Aug. 15. Rags clogging the line triggered the failure. A follow-up investigation traced the source to a construction site where a temporary pumping system had broken down.

When crews returned upstream on Aug. 18 after receiving the bacteria results, they observed additional dead fish and other visual indicators consistent with a sanitary sewer overflow, the release stated.

CCWS Director Alicia Giddens' office issued the notification under Georgia Environmental Protection Division rules requiring public disclosure of sewer overflows into state waters.

Sixth overflow in August

The county's CMOM program page lists at least six separate sewer overflows in August alone, affecting Olley Creek, Clay Branch, Noonday Creek, Piney Grove Creek and a Walden Creek tributary. The day after the Milford Church Road spill, a Sunday, Aug. 16 overflow at 4862 Conductor Way in Mableton sent 720 gallons into Clay Branch via Floyd Lake. No fish kill was observed there.

The 25,000-gallon volume dwarfs every other documented August overflow. It also far exceeds two earlier 2026 spills into Olley Creek tributaries: 490 gallons on Jan. 29 at County Services Parkway and 190 gallons on May 6 at Wellborn Way. Neither of those produced a fish kill.

What's still unknown

The press release does not identify the construction company responsible for the failed pump. No swim advisory or fishing restriction for Olley Creek has been publicly announced, and no timeline for follow-up monitoring results has been disclosed.

CCWS stated that staff will continue monitoring the affected area and that required spill monitoring procedures remain in place.

Residents who observe sewer overflows or have questions can contact the CCWS System Maintenance Division weekdays from 7 a.m. to 3:30 p.m. at 770-528-8731.