20 Metre Ridge

Meet the site

The 20 Metre Ridge is an offshore reef north of Rottnest described by marinelife.org.au as a ridge at 20 m surrounded by a flat reef at 32 m, a couple of kilometres offshore. It is one of the deeper reef sites listed around the island, and the kind of site used by experienced Perth divers looking for bigger fish away from the busy inshore reefs.

Offshore ridges like this tend to attract demersal species such as dhufish and pink snapper, along with samson fish and kingfish in the water column, and the reef surfaces carry sponges, gorgonians and encrusting growth that are better developed than on shallow, surge-swept reefs. Visibility is often good because of the distance from shore.

With a minimum depth of 20 m and surrounding reef at 32 m, the site requires deep training or experience and careful attention to no-decompression limits; nitrox is recommended for the ridge and air or suitable nitrox for any excursion deeper.

It suits advanced divers with their own boat who are comfortable in open water and want a quieter, deeper reef dive within an hour of the metropolitan boat ramps. Leave a competent person on the boat, carry a DSMB and plan for current, which can pick up quickly on offshore reefs. Two short dives are better than one long one here, with a long surface interval between them.

What you might see

Dhufish, pink snapper, samson fish, yellowtail kingfish, buffalo bream, sponges, gorgonians

Location

Reef ridge at about 20 m surrounded by flat reef at 32 m, a couple of kilometres offshore north of Rottnest.