Rocky Bay is one of Rottnest's more remote snorkel spots, near Narrow Neck on the north-west of the island. The Rottnest Island Authority lists it among its six best, describing a rocky expanse that gives way to clear blue lagoons, with schools of fish, coral formations, sea turtles, stingrays and octopus, and a peaceful, less crowded atmosphere; SeaLink calls it a hidden gem with unique underwater rock formations.

The lagoons are protected by the outer rocks and reef, so on the right day they offer calm, clear, shallow water with a surprising range of life, while the outer reef takes the swell. Beyond the bay lies Horseshoe Reef, where the Mira Flores was wrecked in 1886, a reminder of how dangerous this coast is in bad weather.

It suits confident snorkellers willing to make the long ride, and families on calm days who stay in the lagoons. It is too remote and shallow for most scuba divers, who would do better to dive the offshore wrecks and reefs from a boat.

Check the wind before setting out: Rocky Bay needs north-east to north-west winds, the opposite of the south-facing bays, so on a calm northerly morning it can be superb when the north-coast bays are choppy.

The north-west end of Rottnest is where most of the island's historic shipwrecks lie, on the shallow reefs between City of York Bay and Narrow Neck, and the coastline here is wilder than the north-east bays near the settlement. The Rottnest Island Reserve bans spearguns and handspears across all island waters.

Cycle 10-14 km (30-45 minutes) west from the settlement toward the West End, or take the Island Explorer bus to Stop 13. Leave bikes at the top and walk down to the bay; entry is from sand pockets into the lagoons behind the rocks. Snorkel gear can be hired in the settlement; scuba divers must bring filled cylinders from Perth on the ferry, as there are no fills on the island.

SeaLink lists north, north-east and north-west winds as suitable - Rocky Bay faces south-west, so it needs offshore northerly winds; south-westerly sea breezes and swell make it rough. Go on calm mornings. General pattern at Rottnest: summer brings calm morning easterlies followed by a strong south-westerly sea breeze from late morning, so dive early; winter brings north-westerly fronts and large swell, with clear, calm spells between them.

Check the Bureau of Meteorology coastal forecast for swell height and period before committing.

Enter at a sand pocket, snorkel the protected lagoons behind the rocks, and do not swim out beyond the outer reef where swell breaks. Snorkellers should stay within easy reach of the exit point and swim with a buddy; scuba divers at these depths need no safety stop but should ascend slowly and surface near the float.

No operator needed - self-guided snorkel/shore dive. Snorkel gear hire from Pedal & Flipper and other outlets in the Thomson Bay settlement; guided snorkel tours (Rottnest Snorkel) run from Thomson Bay. Scuba divers bring cylinders from Perth - no fills on the island.