Researchers from Deakin University and Parks Victoria have been surveying the Wilsons Promontory seabed using multi-beamed sonar mapping technology.
Until now, the landscape under the waves at Wilsons Promontory has been a mystery.
But the sea floor's secrets have been uncovered by researchers from Deakin University and Parks Victoria.
Marine ecologists and engineers spent six weeks surveying the seabed using multi-beamed sonar mapping technology.
They found unexpected features such as a 30-metre-high underwater sand dune and holes in rock up to 90 metres deep.
Ancient waterways dating back 20,000 years, when the area was above water and linked the mainland to Tasmania, have also been found 60 to 70 metres below the surface.
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Deakin University marine scientist Daniel Ierodiaconou said the findings were unexpected.
''The amount of structure and variation in the detail surprised us all,'' he said.
''We expected to see something but we just didn't expect it to be so visually incredible.''
Parks Victoria marine science manager Steffan Howe said he was interested to learn that not all of the sea floor was composed of sand.
''It looks like we have large areas of reef, which is potentially important because with a hard bottom we have the potential for more plants and animals,'' he said.
''You can get really diverse communities of sponges, hard and soft corals and sea squirts.''
Among the creatures to call the area home are the Australian fur seal, the southern sand octopus, red velvet fish and orange sponge.
Wilsons Promontory sea mapping
The maps generated from the sea floor survey will inform the management of the 15,580 hectare site, Victoria's largest marine national park.
''This information is filling a really important gap,'' Dr Howe said.
''We need to know what's down there to understand how to manage the park better.''
For example, marine ecologists know that the northern Pacific seastar - one of Australia's biggest marine pests, which was found in Tidal River last year - prefers to live in a sandy environment.
The survey allows targeted monitoring of sandy habitat.
An introduction to marine habitat mapping in Victorian Marine protected areas.
For more than 120 of them, the marine park is the furthest part of their distribution range.