The offshore reefs off the West End of Rottnest are the deepest and wildest regular dive grounds around Perth. Marinelife.org.au describes depths of 18-30 m, among the deepest reef dives near the city, over flat sections broken by spires up to 10 m high and deep fissures. Fish life is described as prolific and interesting, with deeper-water species, large groupers, dhufish, schools of kingfish and mackerel, and the possibility of sharks and even a passing migrating whale. Visibility is sometimes very clear and typically 10-20 m.

The West End Demersal Sanctuary Zone covers this end of the island to protect bottom-dwelling species such as western rock lobster and dhufish, which is part of the reason fish are so abundant. Specific named sites in the area include Shark Cave, Tuna Hut, Cathedral Rocks and the 10 Metre Spire, which have their own entries.

These are serious dives: the swell is usually large, currents are strong, and the site is far from shelter and help. They suit Advanced divers with deep and drift experience diving from a well-crewed boat. On the right day they offer a sense of wilderness diving on Perth's doorstep that the sheltered north-east reefs cannot match.

Plan for a long day, carry spare gas and safety gear, and have a sheltered fall-back site in mind.

The West End is about 30 km from Fremantle; marinelife.org.au calls it the furthest most people dive offshore in WA. Allow 1.5-2 hours by boat and pick a day of light easterlies and low swell. Charters schedule West End trips at short notice; private boats should travel in company.

Rottnest lies about 18 km west of Fremantle; allow 45-90 minutes each way by charter or trailer boat depending on the site. Follow Rottnest Island Authority mooring and anchoring rules - do not anchor on reef or in sanctuary zones - carry a marine radio and log a trip plan, as the crossing of Gage Roads can turn rough when the afternoon sea breeze arrives.

Long boat ride to an exposed site with typical swell of 2-3 m and big currents (marinelife.org.au); best near neap tides. Realistically diveable only on a few calm days a year, mostly late summer and autumn, and the afternoon sea breeze makes the return trip rough. 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.

Drop on a spire or fissure edge, dive the reef at 20-25 m as a drift with a live-boat pickup, and ascend on a DSMB before reaching no-deco limits. Agree a turn pressure before descending (half gas, or a third where current is likely), carry a DSMB, and make a 3-minute safety stop at 5 m.

Nitrox strongly recommended; live-boat drift diving with DSMBs.

Occasional West End charters by Perth Scuba and Bucket List Diver on exceptional days (usually Shark Cave, Tuna Hut, Cathedral Rocks); private boats and clubs otherwise.