Northern Arch is perhaps the signature dive of the magnificent Poor Knights Islands. The bottom of the arch itself is at 37 metres but deeper water is close by. Swimming out of the arch to the south, the sandy bottom begins at 45 metres and gradually slopes away.

The northern side of the arch gives better access to deep water with a jumble of enormous boulders quickly dropping down to the sand at around 65 metres. Some small black coral trees can found in this area starting at around 45 metres.

Foxfish (Bodianus sp.) can occasionally be seen lurking beneath the boulders below 60 metres. A deep water relative of the blue cod, the redbanded weever (Parapercis binivirgata) can be found on patches of sand.

Heading to the west from the northern side of the arch towards the point, two large overhaning rock faces are encountered at about 60 metres depth. These are festooned with the precious ivory coral, Oculina virgosa. Unlike Oculina at the Three Kings Islands which appears orange in colour, these coral colonies are mainly white with patches of pink. At the first patch, the coral is coloured pink and white. At the second, it is almost completely white.

A heavily encrusted scooter sits on a ledge at 62 metres a little to the north and west of the arch.

At the point off Northern Arch, the wall plummets in one of the finest vertical descents at the Knights. In places, the wall is almost shear to the sand at 80 metres. Elsewhere, a jumble of huge boulders can be found at 70 to 75 metres leading down to the sand.

The point is a good place to start a dive allowing an easy elevator ride down to the desired depth from where divers can head north and east towards the arch, gradually ascending as the sandy bottom rises up and the vertical rocky wall becomes less steep.

There are remnants of what must have once been majestic black coral trees at 70 metres, their dead branches now festooned with encrusting sponges.

The deep wall is covered in the usual yellow finger sponges and Primnoides gorgonian fans. Some small black coral trees branch out from the wall but they are not a major feature of this area.

The walls to the north of the arch receive more direct sunlight and are the better side to spend time decompressing. Rich encrusting life grows in the shallows which are a productive area for finding unusual tiny nudibranchs.

The anchorage is well sheltered from southwest weather and the site is suitable for divers of all levels.

After a short swim towards the point, divers can descend down the pretty wall which is covered with gorgonian fans. The descent continues by dropping down over a series of huge boulders. Sandy patches between the boulders are reached at around 60 metres depth where an enormous boulder, the size of a double garage appears from out of the gloom. On the outside of this boulder, it's overhanging faces are cloaked in white Oculina at around 67 metres depth. The boulder sits on other large rocks and there is a swim-through underneath it.

Pink coloured clumps of Oculina can be found on vertical rock faces close to the sand which is reached at a depth of about 73 metres. Look out for a large organ-pipe sponge in this area.

At the point, the wall drops steeply to a small plateau at about 40 metres from where you swim out a little before continuing the descent. Between two enormous boulders on the edge of the plateau is a large, healthy black coral tree at about 44 metres depth. It's perhaps two metres across and is one of best coral trees at the Knights in this depth range.

The sandy bottom begins at about 65 metres and gradually slopes away to 75 metres and beyond.

The eastern side of the point (heading towards Southern Arch) offers a much more vertical descent to 60 metres which becomes a jumble of enormous boulders in the 60 to 70 metre range. Foxfish frequent this area and some white Oculina has been found here on an overhanging rock face at 65 metres depth.

As you head in the other direction from the point, towards Calypso Bay, the descent requires considerably more horizontal swimming to reach 60+ metres.

On the deeper parts of the reef, yellow finger sponges and Primnoides gorgonians abound. Small black coral trees can be found from 40 metres with some larger trees from 45 to 60 metres.

Wade's World (North of Labrid Channel, outside Jan's Tunnel)

Named after Wade Doak, the Poor Knights diving pioneer and passionate conservation advocate, this area is arguably the best deep dive site at the Poor Knights.

A finger of jagged reef extends out from the island and tumbles down to more than 80 metres depth. Bathed by nutrient rich currents, the rocky outcrops are covered in black coral trees, sponges and gorgonian fans.

A large, healthy black coral at 62 metres is cloaked in colourful sponges, snake stars, anemones and other invertebrate critters. In several visits over many months, the tree has always had a stinging wandering anemone (Alicia sp.) perched at the end of an upper branch. A small black coral tree nearby (also at 62m) has a large clump of pink and white Oculina growing at its base.