Nepean Bay Inner West is the second of the shallow Point Nepean reefs described in the Parks Victoria divers' guide and listed by Scuba Doctor. It lies at the western end of Nepean Bay, on the inside of the point and only a few hundred metres from the entrance, in 1–5 m, and it is described as 'a series of detached reefs in shallow water' whose undercuts are 'deep' and which is 'full of marine life and a large variety of fish species'.

The detached reefs are limestone outcrops standing on sand, each with kelp on top and a deep overhang eaten into its base by the tide. Those undercuts are the site's distinction: the listing notes that Port Jackson sharks appear here in breeding season in significant numbers, using the deep crevices for shelter, and in late winter and spring a torch pushed into an overhang will often show several of them stacked together, with their spiral egg cases wedged in the cracks nearby. Crayfish share the same shelters. Over the reefs the fish are the same protected-park community as Radar – scalyfin, old wives, moonlighters, wrasse, leatherjackets, sweep – with rays on the sand and cuttlefish in winter.

The listing notes that the site 'is exposed to tidal influences and is best dived on the ebb tide'; its position nearer the entrance means it feels the flood sooner than the eastern end of the bay. It is boat access only, as shore diving is prohibited from Point Nepean. It suits snorkellers on a calm day, Open Water divers wanting an easy, fishy shallow dive, and photographers in the Port Jackson season. Radar lies 270 m to the east and the Petriana wreck 700 m to the south on the ocean side of the point.

Boat access only – Point Nepean is a national park and the listing notes that shore diving is prohibited from the point. Charters from Portsea Pier (Dive Victoria Group, Bayplay) are 5–10 minutes west along the shore; Red Boats from Queenscliff about 15 minutes across the entrance. Private boats launch at Sorrento Boat Ramp (Point Nepean Road, all-tide, trailer parking) and run 15 minutes west past Portsea.

Nepean Bay is shallow and the boat anchors on sand outside the reef line or holds off; a dive flag is required and the pilot boats and ferry pass close to the bay.

Nepean Bay is 'sheltered from all winds except northerlies' (Scuba Doctor) and is the standard fallback when the Heads are unworkable, but the tide still runs through it: the Parks Victoria guide advises diving these reefs on the ebb, when the outgoing tide leaves the bay in relatively still water and any drift sets back toward Portsea rather than out through the entrance. Slack water at Port Phillip Heads does not coincide with high or low water: it falls roughly three hours after high or low water at Point Lonsdale, and the usable window is typically 20–40 minutes. Use the Ports Victoria / Port of Melbourne slack-water predictions for The Heads (also republished by charter operators and WillyWeather 'Rip Bank') rather than a standard tide table.

A northerly over about 15 knots puts a chop on the bay and cuts visibility; swell has little effect. Diveable year-round; clearest in autumn. Water 12–13 °C in winter, 17–19 °C in late summer.

Being at the western end of the bay it is closer to the entrance and feels the tide more than Radar.

Anchor on sand between the detached reefs on the ebb. Work from reef to reef at 2–5 m, looking deep into the undercuts with a torch for Port Jackson sharks and crayfish, and circle back to the boat; snorkellers can duck-dive the undercuts in the calm.

Dive Victoria Group and Bayplay (Portsea) as a snorkel or shallow second dive; snorkel-tour boats; private boats from Sorrento.