The Sisters are a group of limestone reefs at the southern end of Shoalwater Islands Marine Park in Warnbro Sound, marked by rocks breaking the surface. The City of Rockingham lists them as a scuba and snorkelling site in 2–6 m, and the Marine Life Network describes a beginner-friendly dive of about 8 m with ledges and caves.

The reef is typical Warnbro Sound limestone: flat tops covered in kelp and red algae, with ledges, small overhangs and caves around the edges and sand between. Many wrasse species, buffalo bream, sweep, herring cale and leatherjackets move over the reef, and rays rest on the sand. Nudibranchs and sponges grow under the ledges. Resident Australian sea lions from the Shoalwater islands often visit divers here, which is one of the site's attractions.

The historic wreck of the Chalmers, a timber barque lost in 1874, lies in 3 m on the Sisters reef system. Little remains beyond a kelp-covered ballast mound and scattered fittings, but it can be visited on the same trip.

With shallow depths, short boat rides and plenty of structure, the Sisters suit newly certified divers and snorkellers from private boats. They are exposed to south-westerly swell, so choose a calm day. As within the rest of the marine park, check sanctuary zone boundaries before fishing, and give sea lions space.

The Sisters make a good combination with the Saxon Ranger or First Rock for a two-dive morning out of Safety Bay, keeping boat runs short and depths moderate. Published information is limited to two sources, so check depths and anchoring spots on the sounder before descending.

A short boat trip from Rockingham or Safety Bay: launch at the Bent Street (Safety Bay), Carlisle Street, Donald Drive or Port Kennedy ramps. The Sisters lie south of Penguin Island in Warnbro Sound and are marked by rocks breaking the surface. The Marine Life Network advises anchoring on the western side in sand.

The Chalmers wreck lies on the same reef system. Allow 10–15 minutes from Safety Bay.

Warnbro Sound is partly sheltered by the reef chain, but the Sisters are exposed to south-westerly and westerly swell; wait for swell under about 1 m and winds under 15 knots, preferably easterly. The summer sea breeze builds from late morning. Visibility falls after swell or strong winds and is best after several days of easterly weather.

North-westerly winds ahead of winter fronts close the site.

Anchor in sand on the western side, descend and follow the reef edge at 5–8 m, exploring the ledges and small caves, then return across the reef top in 2–4 m to the anchor.

Occasional trips by Rockingham dive schools and clubs; mostly private boats.