Martin Islet, the southernmost of the Five Islands, is the Wollongong dive most people come for in winter, because the island is a haul-out for Australian fur seals. McFadyen counted around 50 on one visit, and between June and October the young animals often come down to play with divers – swooping past, blowing bubbles and nibbling fins – while larger adults patrol above.

The diving is good even without seals. The reef off the island's northern end forms a wall whose top is at 14–15 m and whose base reaches 25–26 m, deepening to about 30 m further north-east. A small gully and channel near the usual anchorage lead out to the wall, and after 8–10 minutes of swimming the wall becomes more prominent as it turns a corner. Its face is covered in sponges, sea squirts and gorgonians that make the site unusually colourful for the Illawarra.

Fish life includes black reef and mosaic leatherjackets, combfish, eastern blue groper, striped seapike, ladder-finned pomfret and swarms of one-spot pullers, with Port Jackson sharks resting on the reef through autumn and winter. The rocks carry a good variety of nudibranchs. Because the best part of the wall is below 20 m, the site suits Advanced divers, and the simple out-and-back route along the wall makes navigation easy. Seal encounters are best enjoyed by staying still near the bottom rather than chasing the animals; they lose interest in divers who pursue them. Treat the haul-out rocks as off-limits – the island is part of the Five Islands Nature Reserve and landing is prohibited.

Launch from the Port Kembla boat ramp in the Outer Harbour (behind the steelworks; large car and trailer park, toilets). Wollongong Harbour's ramp (Belmore Basin) is closer to the northern islands but suits only small boats in calm seas. From Port Kembla steer out through the harbour entrance, keeping clear of the shipping channel, and head for the island; the run is 10–15 minutes in a small boat.

From the harbour entrance head south-east to the northern end of Martin Islet, the southernmost island of the group. Anchor near the small gully and channel system at 34° 29.611' S 150° 56.313' E; the reef top is 14–15 m with sand 20–30 m out from the wall.

The Five Islands sit in open water off Port Kembla and are exposed to all swell, but the islands themselves give lee on one side or the other: dive the northern ends in southerly swell and the southern ends in north-easterly conditions. Boats generally want less than about 1.5–2 m of swell and winds under 15 knots for the short run out of Port Kembla Outer Harbour; Wollongong Harbour's ramp is suitable only for small boats in calm seas. Visibility is often better than the inshore beaches, but drops after heavy rain when Lake Illawarra, Allans Creek and the harbour flush brown water out.

Best visibility is usually late autumn to early winter; winter westerlies produce flat seas. Martin Islet is the most southerly and exposed island; its northern end gives shelter from southerly swell but is rough in north-easterlies.

Swim out through the channel from the gully and follow the wall north-east. After 8–10 minutes the wall becomes higher as it turns left around a corner; continue to your turn point at around 25–28 m, then return along the top of the wall near the kelp line. On air expect about 27–28 minutes of no-deco time.

If seals are present, stay low near the bottom and let them come to you.

Expedition Dive (Sydney) runs dedicated seal trips on weekends from early June to October/November; United Divers (Wollongong) visits when numbers allow; also a favourite with private and club boats.