Which of these islands is not found within the waters of Port Jackson, Australia?

Magnetic Island is an island 8 kilometres (5 mi) offshore from the city of Townsville, Queensland, Australia. This 52 km2 (20.1 sq mi) mountainous island in Cleveland Bay has effectively become a suburb of Townsville, with 2,335 permanent residents. The island is accessible from Townsville Breakwater to Nelly Bay Harbour by ferry. There is a large 39.5 km2 (15.3 sq mi) National Park and bird sanctuary and walking tracks can be taken between the populated bays and to a number of tourist destinations such as the World War II forts.

Port Jackson, consisting of the waters of Sydney Harbour, Middle Harbour, North Harbour and the Lane Cove and Parramatta Rivers, is the ria or natural harbour of Sydney, New South Wales, Australia. There are several islands within the harbour, including Shark Island, Clark Island, Fort Denison, Goat Island, Cockatoo Island, Spectacle Island, Snapper Island and Rodd Island.