Sow and Pigs is the reef every Sydney sailor knows and almost no diver visits: a low rock platform in the middle of the outer harbour, just inside the Heads, that has claimed at least six ships since 1788 and is now fenced by four cardinal beacons. It is about 150 m long and 70 m wide, oriented north-west to south-east, and rises from a maximum of 8 m on its western side to 4–5 m across the northern and north-eastern sections, where the 'pigs' break the surface at low tide. The western edge is an almost straight low wall; elsewhere the reef is a mass of cracks and overhangs with a couple of tight swim-throughs, and a substantial concrete block on the western side is probably the base of an old channel marker.

Jewel anemones colour the undersides of the ledges. Because it sits in the tidal stream between the Heads and is fished constantly, one expects dense fish life; in fact bream, luderick and blue groper are present but not in the numbers the position suggests, and whiting work the surrounding sand. The interest is the setting – a reef in mid-harbour with the Heads on one side and the city on the other – and the history: fragments of old wreckage and anchors turn up in the cracks.

It is shallow enough for Open Water divers and snorkellers, but the logistics are for experienced boat handlers: ferries and ships pass close on both sides, tidal current runs across the reef, and the best days coincide with the fishing fleet. Dive it on the last of the flood, stay inside the markers and surface on the anchor line. Sow and Pigs suits harbour boat owners looking for something new, night divers, and anyone curious about the most infamous rock in Port Jackson; a full circuit takes 30–60 minutes.

Boat only, in the centre of the outer harbour halfway between Watsons Bay and Middle Head, 5 minutes from Rose Bay wharf or Watsons Bay, 15 minutes from Little Manly. The reef is ringed by north, south, east and west cardinal markers; anchor inside them on the southern or western side (anchor mark 33°50.20'S 151°16.26'E WGS84). The main shipping channels pass either side, and the reef is often occupied by anchored fishing boats, which can make it undiveable.

Exposed to swell entering the Heads from the east and south-east and to chop from any strong wind, but shallow enough that only the surge matters; dive it in under 1 m swell. Tidal streams run across the reef and are strongest mid-tide, so plan for the last two hours of the flood, which also brings the cleanest water – visibility is 5–7 m normally and up to 25 m on a big blue-water flood. Run-off after rain ruins it.

Fishing boats anchored on the reef and ferry/ship wash from both channels are the main practical obstacles.

Anchor on the western side in 8 m and circumnavigate the reef clockwise, following the base along the straight western edge, round the shallow northern end at 4–5 m, and back along the eastern side through the overhangs and the two tight swim-throughs, checking the big concrete mooring block on the west. Thirty to sixty minutes covers the whole reef; stay within the cardinal markers and ascend on the anchor.

No regular operator. Private boats and clubs; occasionally used by Rose Bay-based charters as a shallow second dive or training site when the Heads are rough.