Middle Grounds is a reef in the middle of the entrance to Jervis Bay, inside the bay itself, roughly between Darts Point and Bowen Island. McFadyen summarises it succinctly: the reef is quite extensive, spreading for some distance in a north-west to south-east direction, but it only rises a metre or two off the sand. It is essentially an island of rock in a sand plain, stepping down gently towards the ocean, at around 24 m.

The low profile means there are no walls or caves; instead the attraction is a long band of rock carrying sponges, sea squirts and ascidians, with fish that gather wherever there is structure in the sand – leatherjackets, sweep, wrasse and small schools of yellowtail – and rays, flathead and other sand dwellers on its margins. Cuttlefish and nudibranchs can be found on the ledges.

The site's main value is availability. Because it lies inside the entrance, it is often possible to dive here when every other site except North Bowen Island is closed by huge southerly seas, making it a useful option for operators and visitors on marginal days. McFadyen admits he had dived it only once and remembered little, so published detail is thin and confidence is moderate. Divers should note the depth (around 24 m), which makes it better suited to Advanced divers, and the possibility of current across the entrance on big tides. It is a simple, relaxed dive in otherwise poor weather rather than a destination, and a compass is useful because the low reef offers few landmarks.

Charters depart Huskisson; private boats launch at Huskisson, Callala Bay or Murrays Beach. Head for the middle of the entrance, roughly on a line between Darts Point and Bowen Island (15 minutes from Huskisson, 5 minutes from Murrays). McFadyen gives 35° 06' 29" S 150° 46' 00" E on the AUS66 datum – about 220 m from a WGS84 position – so use the sounder to find the reef rising a metre or two off the sand.

Middle Grounds sits inside the bay entrance and is often diveable when huge southerly seas have closed everything except North Bowen Island. A strong south-easterly swell running straight in through the entrance will affect it. Tidal current can run across the reef on big tides.

Visibility is typically 10–20 m.

Descend to the reef at about 24 m and follow its long axis north-west to south-east, looking over the low ledges; turn at half gas or no-deco limit and return along the other edge.

Dive Jervis Bay (Huskisson; boats Avalon and Genesis) runs double boat dives most days, and Deep 6 Diving Jervis Bay / other Huskisson operators also visit; site chosen on the day according to swell and wind. Chosen mainly when big southerly seas close other sites.