South Bristol Harbor in South Bristol is located between Bristol Neck and Rutherford Island, along the narrow passage known as "The Gut" that connects the Damariscotta River to the west and Johns Bay to the east. The harbor is 40 miles northeast of Portland and about 14 miles southeast of Bath. The business section and commercial fishing center of South Bristol are located along both sides of the harbor. A boatbuilding firm, seasonal passenger vessels and a small recreational fleet also utilize the waterway.

Work in South Bristol Harbor was completed in two stages. In 1914, the Corps removed obstructing ledges to a depth of two feet through the drawbridge (replaced by a swing bridge in 1930) or. Route 129. In 1963, the Corps constructed a sixfoot-deep channel through the swing bridge. The channel has a width of 50 feet on the Johns Bay side of the bridge, narrowing to 20 feet under the bridge, widening again to 50 feet as it extends southwesterly toward the Damariscotta River.