The county is divided between two major basins. Most runoff flows into the Middle Chattahoochee-Lake Harding and Upper Chattahoochee River sub-basins of the ACF River Basin (Apalachicola-Chattahoochee-Flint River Basin) along the southeastern border, directly via Willeo Creek, Sope Creek (Sewell Creek), Rottenwood Creek (Powers Creek, Poorhouse Creek, Poplar Creek), Nickajack Creek and others. The large Sweetwater Creek is the other major stream, carrying the waters of Noses Creek (Ward Creek, Olley Creek, Mud Creek), Powder Springs Creek (Rakestraw Creek, Mill Creek) and others into the Chattahoochee. A ridge from Lost Mountain in the west, to Kennesaw Mountain in the north-central, to Sweat Mountain in the extreme northeast, divides the far north-northwest of the county into the Etowah River sub-basin of the ACT River Basin (Coosa-Tallapoosa River Basin), which includes Lake Allatoona. Noonday Creek (Little Noonday Creek) flows northward into the lake, as does Allatoona Creek, which forms a major arm of the lake. Proctor Creek forms the much older Lake Acworth, which in turn empties directly into Lake Allatoona under the Lake Acworth Drive (Georgia 92) bridge. North Cobb is in the Coosa River basin.