Swan Bay is a shallow coastal lagoon of about 30 square kilometres located in Victoria Australia between Queenscliff and St Leonards on the traditional lands of the Wadawurrung. Swan Island is about 1.4 square kilometres and connected to the mainland at Queenscliff via a bridge and a causeway.

Both Swan Bay and Swan Island are important sea and landscapes that have significant ecological, historical, recreational, and cultural value.

The island has a long military history from the 19th century when it was fortified to protect the entrance to Port Phillip to its current use from 1961 by the Department of Defence and the Australian Secret Intelligence Service for training. It is also home to the Queenscliff Cruising Yacht Club and the Queenscliff Golf Club.