Devils Drop Off is named for the southern blue devil, the placid, vivid-blue reef fish that sits in the overhangs of every Heads wall and is especially reliable here. The Scuba Doctor listing describes 'a huge drop-off from 12 to 30 metres' that then 'continues with a series of ledges, overhangs and swim-throughs' to 55 m, and picks out one feature: at 27 m 'a long overhang to follow covered in a large variety of soft corals and small fans'.

The site is on the Nepean side of the entrance, just inside the Heads and close to the tip of the point, where the ebb runs hardest. That is why the listing restricts it to the ebb slack and the neighbouring Abyss listing describes the area as diveable only at 'slack water turning to a flood' – the very end of the ebb, so that the flood, when it comes, carries divers back toward Portsea. The initial drop from 12 to 30 m is steep enough to be dramatic on the first descent, and the 27 m overhang is long enough to occupy most of a slack-water dive on its own; below it the wall continues in steps to 55 m for those with the training.

Beyond the blue devils the listing records longsnout boarfish, Port Jackson sharks, southern fiddler rays (banjo sharks) and other rays on the ledges and sand, and the soft-coral and gorgonian cover is among the best on the Nepean side. Seals from the Point Nepean haul-out are frequent. It is a regular on Portsea charter schedules when the ebb slack falls at a workable time, and is a favourite with photographers for the overhang. One caution: the Scuba Doctor coordinates are flagged as believed incorrect, and the site should be dived with a skipper who knows the drop.

Boat access only. Charter boats leave from Portsea Pier (Dive Victoria Group, Bayplay) and Queenscliff Harbour (Dive Victoria Group, Red Boats); run time is about 12 minutes. Private boats launch at Sorrento Boat Ramp (Point Nepean Road, Sorrento, all-tide concrete ramp with trailer parking) or Queenscliff Boat Harbour ramp (Larkin Parade, Queenscliff), roughly 12 minutes to the site.

The site is just inside the Heads off the tip of Point Nepean, 10–12 minutes west of Portsea Pier; the Scuba Doctor GPS is flagged as 'believed to be incorrect', so rely on a skipper who knows the drop. Skippers must call Lonsdale VTS (Point Lonsdale) or listen to VHF 12 for shipping movements before dropping divers, and must carry a dive flag; anchoring is not permitted in the shipping channel, so a live boat and a drop-shot or drift float is the normal method.

It is dived only on slack water at the end of the ebb (SWE); on other tides the current across the site is unworkable. 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.

Being outside or right at the entrance, it is exposed to Bass Strait swell: anything over about 1.5 m from the south-west or south, or a strong southerly/westerly wind against the ebb, produces standing waves in The Rip and charters cancel. Northerlies flatten the entrance and give the best days. Visibility is best in late summer and autumn (Feb–May) when the water is clear and the westerlies have eased; winter brings 11–13 °C water and bigger swells but often the clearest days after a run of settled weather.

Heavy rain has little effect this close to the ocean. Scuba Doctor lists it as ebb slack only; the neighbouring Abyss listing notes the area is 'prone to strong currents and swells and can only be dived during slack water turning to a flood', i.e. the very end of the ebb.

Shot onto the reef at 12 m at the ebb slack. Drop the face to the long overhang at 27 m and follow it, torch on, for the soft corals and fans, then continue along the ledges and swim-throughs at 25–30 m. Turn before the flood begins, ascend the drop-off to 12 m, DSMB and drift inside on the young flood.

Continues to 55 m; nitrox for the 27 m overhang; ebb slack – deco drifts inside on the flood.

Dive Victoria Group (Portsea and Queenscliff) – double boat dives to the Heads walls most days of the week, site chosen on the morning by slack-water time and swell; Bayplay Adventure Tours (Portsea) – weekend and holiday charters; Red Boats (Queenscliff) – weekend Heads charters; Melbourne clubs (VSAG, Power House Underwater Club, Scuba Diving Melbourne) run their own boats here regularly.