Fish Bowl is Norfolk Island's best-documented dive, thanks to Nigel Marsh, who describes it as 'a pretty rock and coral reef with numerous caves, ledges and overhangs' at Nepean Island, with a maximum depth of 18 m. On his dive the visibility was close to 40 m and eight Galapagos sharks patrolled the reef, which gives an idea of why local divers rate it.

The name suits it. Marsh records schools of damsels, fusiliers, trevally and kingfish over the reef, with a busy mix of reef fish below. The caves and ledges hold the smaller and more secretive species: goldribbon cod – a striking yellow-striped grouper – striped boarfish, morays and slipper lobsters. On the sand a blotched fantail ray is possible, and nudibranchs add macro interest. Norfolk's fish fauna mixes tropical, subtropical and temperate species with New Zealand and Lord Howe elements, and several fish are found only in this corner of the Pacific.

Nepean Island itself is a small limestone and basalt island about 1 km south of Kingston, part of Norfolk Island National Park, and the reef around it is within the Special Purpose Zone of the Norfolk Marine Park that surrounds the island. Norfolk's reefs are described as largely pristine, with plate corals, soft corals, sponges and black coral trees, although coral cover is patchy compared with a tropical reef.

The dive suits Open Water divers in calm conditions, and the caves are open overhangs rather than true penetrations. Because Nepean lies off the south coast, it is dived when the wind is northerly or light and the southerly swell is down. Diving on Norfolk is run by a small part-time operator, so book well ahead.

Norfolk Island is about 1,450 km east of Brisbane; flights run from Sydney and Brisbane (about 2.5 h; check the current carrier). A hire car is essential. Norfolk has no harbour: Norfolk Island Diving's open boat is lowered by crane from Kingston Pier (south coast) or Cascade Pier (north-east coast), whichever is in the lee of the day's wind, and divers board from the pier steps once it is in the water.

For the Nepean Island sites the boat launches at Kingston Pier and runs about 1 km south to Nepean Island – a trip of 5–10 minutes. Nepean is a small, uninhabited island within Norfolk Island National Park; landing is not part of the dive.

Norfolk's south coast, including Kingston, Nepean Island and Phillip Island, faces the prevailing south-east trade winds and southerly swell, which are strongest from May to September. A south-easterly over about 15 knots or a southerly swell above 1.5–2 m makes the boat launch at Kingston Pier unworkable and the southern sites rough; they are dived on northerly or light-wind days, often in summer. Surge is felt in caves and gutters with any swell.

Visibility is typically 20–40 m and can exceed 40 m in winter. There are no stingers, and cyclones rarely reach this far south, though ex-tropical lows can bring big seas in summer and autumn.

Descend onto the reef at 12–14 m and work slowly along it, looking into caves and under ledges for goldribbon cod, slipper lobsters, morays and striped boarfish. Watch the blue for Galapagos sharks and schooling kingfish and trevally. Turn at half air, return at 8–10 m and ascend on the boat's line or under an SMB.

Norfolk Island Diving (local instructor James and divemaster Mitch Graham) – small open boat craned in at Kingston or Cascade Pier depending on wind; runs part-time, mostly weekends, so book ahead by email (norfolkislanddiving@gmail.com).