Captain Nitro Drop Off is the western end of Spectacular Reef on the Queenscliff side of the Heads, and its name – a nod to the nitrox-diving identity who put it on the map – tells you which community dives it. The Scuba Doctor listing gives a range of 16–60 m and describes 'a series of walls that plunge to over 60 metres in 5 to 10-metre increments' with 'huge boulders the size of houses' at the foot of the steps.

The terraced structure is the same as the rest of the Heads walls, but the boulders set this site apart: whole slabs of the cliff have fallen away and lie stacked below the faces they came from, creating canyons, roofed gaps and shelters that the smaller fish and the crayfish use. The listing records large southern rock lobster and – 'a rare Victorian sight' – both red morwong and blue morwong on the terraces, along with the usual blue devils, boarfish and old wives, and notes that seals and dolphins pass through the mid-water above the wall.

The site lies in the shipping channel, so it is dived on slack water 'subject to shipping': the boat obtains a shipping report and the dive is abandoned if a vessel is due during the window. There is no shallow retreat above 16 m, and the 60 m base makes it, with North Wall next door, one of the standard trimix walls on the Queenscliff side. For recreational Advanced divers the first two terraces at 20–30 m offer a full dive on their own, and the sheltered position inside the bay means it is often workable when the Lonsdale sites are not. It is dived mostly by clubs and by Queenscliff-based charters on request rather than as a scheduled 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 10 minutes to the site.

The site is at the western end of Spec Reef off Shortland Bluff; an alternative mark is -38.288, 144.663167. 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, either at the end of the flood (SWF) or the end of the ebb (SWE); most operators prefer the flood slack so that any residual current sets into the bay rather than out to sea. 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.

Inside the Heads it is sheltered from most swell, but a south-west swell over about 2 m still surges across the top of the wall and a westerly or south-westerly wind over 15–20 knots makes the boat work unpleasant; big seas outside drop visibility to a few metres for a day or two. 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.

Listed as 'slack water subject to shipping' – the dive is scrubbed if a ship is due through the entrance during the window.

Shot onto the 16 m reef top at slack. Step down the walls – each plunges 5–10 m to the next terrace – to the planned depth, weaving between the house-sized boulders at the base of each step; hold 30 m for a recreational profile. Return up the terraces to the top, DSMB and drift.

Base 60 m+; trimix; shipping-subject slack; drift deco under DSMB with tracking boat.

Dive Victoria Group (Portsea/Queenscliff) – runs the deep Heads walls for advanced and technical divers on suitable slack-water days; Red Boats (Queenscliff) – deep-wall and technical charters on request; otherwise private club boats (VSAG, Power House Underwater Club, Scuba Diving Melbourne). Not a routine training-boat site.