The Arches Marine Sanctuary (48ha) is located  offshore in 20m of water to the south of Port Campbell township. This area is characterised by high energy waves and cool water from the Southern Ocean that have also shaped the nearby Twelve Apostles.

Reefs within the Marine Sanctuary consists  of  spectacular  dune limestone formations such as canyons, tunnels, arches, caverns, ledges and vertical sink holes in 19-25m of water which support a diverse range of algae, sponges, bryozoans, hydroids, gorgonians and sea stars characteristic of deeper Bass Strait waters.

The upper surfaces of the arches are covered with kelp and an understorey of red seaweeds while the  undersides and canyon walls provide habitat for sessile invertebrates making this a spectacular dive site when conditions allow.

The walls are covered with arrangements of colourful creatures including large red and orange sea-fans that emerge vertically from the rock, stinging hydroids that form feather-like colonies, and delicate lace corals, sponges, and gelatinous tunicates of a variety of shapes and colours cover many surfaces. 

Fish species seen here are typical of those found in western Victoria at places like the nearby Twelve Apostles Marine National Park, however The Arches Marine Sanctuary is also notable as an important site for Port Jackson Sharks that are frequently seen during the day sleeping under ledges within the park.