South Channel Fort, also known as South Channel Island, is a 0.7 ha artificial island in southern Port Phillip, Victoria, Australia, 6 km north-east of the town of Sorrento. It was part of a network of fortifications protecting the narrow entrance to Port Phillip.
It is 122 m long, 76 m wide, and is 6.4 m above sea-level. It was built on a shoal, close to the main shipping channel of the bay, with 14,000 tonnes of bluestone boulders, concrete and sand. It was constructed during the 1880s as part of a defensive strategy to protect and control access by sea to Port Phillip and the cities of Melbourne and Geelong. It still contains remnants of its original military equipment, including disappearing guns.