Mary Cove is a small, quiet south-coast cove listed in SeaLink's guide to Rottnest snorkelling as a picturesque spot with clear waters and rocky outcrops that avoids the crowds, with bream, snapper and occasional sea turtles. It lies west of Salmon Bay on the road toward the West End, far enough from the settlement to keep visitor numbers low.

The cove's limestone outcrops break up the sand and seagrass, giving shelter for reef fish and invertebrates close to shore, and the south coast's clear water and Leeuwin Current influence mean a mix of temperate and tropical species. It is a snorkel rather than a scuba site.

It suits confident snorkellers cycling the south coast who want a quiet spot. Because it faces the Southern Ocean, conditions depend heavily on swell rather than just wind: SeaLink's list of suitable winds is generous, but any significant southerly swell will make the cove surgy. On a calm day, however, it is an attractive and uncrowded swim.

Published detail is limited to the SeaLink listing, so depths and coordinates are approximate. Bring water and sun protection, as there are no facilities.

Mary Cove combines well with Salmon Bay and Little Salmon Bay on the way back to the settlement, choosing whichever is calmest.

Rottnest's south coast is where the warm Leeuwin Current has most influence, which is why the corals and tropical fish in these bays are unusual for a location so far south. The Rottnest Island Reserve bans spearguns and handspears across all island waters. The general rule is simple: in a northerly or easterly, snorkel the south side; in a southerly, go to the north-coast bays instead.

Cycle west along the south coast road beyond Salmon Bay (roughly 9-10 km from the settlement) or use the Island Explorer bus, then walk down to the cove from the road. Enter from the sand between the rocky outcrops. 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 all winds except southerly as suitable (N, NE, E, SE, SW, W, NW), but the cove faces the south coast swell: dive only when swell is low. 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.

Snorkel around the rocky outcrops within the cove, returning to the beach; do not venture beyond the cove in swell. 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.