The Mud Islands reserve is located within Port Phillip, about 90 km south-west of Melbourne, Australia, lying 10 km inside Port Phillip Heads, 7 km north of Portsea and 9 km east of Queenscliff. The land area of about 50 ha is made up of three low-lying islands surrounding a shallow tidal 35 ha lagoon connected to the sea by three narrow channels. The shapes and configuration of the islands change over the years due to movement of sand by tidal currents.