Flinders Ocean Beach – Flinders Back Beach to divers – is the stretch of ocean coast on the south-western side of West Head, between the Mushroom Reef Marine Sanctuary and the cliffs below the Flinders golf links. What the shore dive offers is a continuation of the sanctuary's basalt and limestone reef outside the no-take boundary: kelp-covered ledges and gutters running out from the beach, sponge and ascidian growth on the shaded faces, and the fish community of the exposed Flinders coast – sweep, zebrafish, old wives, morwong, leatherjackets, cowfish and wrasse over the reef, Port Jackson sharks under the ledges, weedy seadragons on the kelp margin and rock lobsters and abalone in the crevices. Because it lies beside a sanctuary the fish life is better than most fished reefs, and because it lacks the sanctuary's signage and rock pools it is far less visited.

Its difficulty comes entirely from the sea: south-westerly exposure, strong tidal currents around West Head, rips on the beach and surge on the reef, which is why it carries an Advanced rating despite the modest depth. A diver planning it should watch the reef for ten minutes before gearing up and treat any white water as a veto. On the right day it combines naturally with Mushroom Reef and Flinders Pier for a full day at Flinders.

It suits experienced divers who enjoy exposed shore reef with strong life and no crowds; it is not a beginner or a casual snorkelling site.

From Flinders village take Golf Links Road to the Flinders Ocean Beach car park at the western end (also the access for Mushroom Reef), a short track and steps down to the sand. Enter from the beach at the eastern end, away from the sanctuary's intertidal platform, and swim out to the reef in 4–8 m; the sanctuary boundary lies to the west, so know where you are if you intend to take anything (better not to). Exit onto the beach.

Faces south-west into Bass Strait and shares Mushroom Reef's exposure: diveable only with offshore north-easterly to north-westerly winds and a low, long-period swell; south-easterly through south-westerly winds and any rough weather produce breaking waves on the reef and heavy surge. Currents around West Head are strong on the running tide, so dive near slack water. It is an unpatrolled beach with rips; the WillyWeather Flinders Ocean Beach forecast is the reference.

Summer afternoons are ruled out by the sea breeze.

Enter at the eastern end of the beach near slack water, swim out to 4–5 m and follow the reef seaward and east with the rock on your left, exploring kelp-covered ledges to 8 m. Turn at half gas or when current builds, return along the same line and exit onto the beach.

No regular operator; occasional Scuba Doctor guided dives and Peninsula clubs. Ian Lewis's 'Shore Dives of Victoria' (3rd ed., pp. 128–129) is the standard reference.