Yena Gap Outer Reef is a useful rather than spectacular site that earns its place because it can be dived when most of Sydney is blown out. It lies off the Yena Gap picnic area in the Captain Cook's Landing Place section of Kamay Botany Bay National Park, just south of the bay entrance, and is too far out to reach from the shore. The reef forms a kind of rocky island: running in from deeper water the depth comes up from about 22 m to 15 m, falls back to 22 m and rises again to 18 m, the dip being a sand finger or gutter that extends into the reef for at least 100 m.

The eastern wall is the more prominent, dropping to about 23 m on sand with small overhangs along its face. The western wall, on the other side of the gutter, is lower and less defined, broken by small cracks and larger boulders and carrying more kelp. The reef top has patches of kelp with sponges, sea squirts and encrusting growth between, and invertebrates are the main interest: nudibranchs (McFadyen notes yellow species), starfish and biscuit stars.

Fish life is the usual Kurnell mix of sweep, yellowtail, leatherjackets and morwong. The layout is easy to navigate, with the sand gutter acting as a handrail between the two walls. What makes the site valuable is its shelter – it is one of the few decent boat dives in Sydney that can safely be done in strong southerly or even south-easterly winds, when the Eastern Suburbs and Royal National Park coasts are unworkable.

McFadyen sums it up as a nice dive, but not an outstanding one, worth doing when the weather rules out your preferred site. It suits Advanced divers, clubs and private boat owners looking for a reliable bad-weather option 15 minutes from the Botany Bay ramps.

Boat only – the Kurnell cliffs are sheer and in Kamay Botany Bay National Park, with no practical shore entry. From Botany Bay, launch at Kyeemagh (Cooks River), Foreshore Road or Bonna Point (Silver Beach, Kurnell), run out past Captain Cook's Landing Place, Inscription Point and The Leap, then turn south along the cliffs; from Port Hacking (Gunnamatta Bay/Tonkin Park or Lilli Pilli ramps) run out past Bass and Flinders Point and north-east along Bate Bay past Cronulla Beach and Cape Baily. From the Botany Bay ramps it is 10–15 minutes out the heads and south past The Leap to off the Yena Gap picnic area.

The site is too far out to shore dive. Go to McFadyen's GPS mark and run in towards the shore; the depth comes up from about 22 m to 15 m, drops back to 22 m and rises again to 18 m – anchor on the first rise.

This is one of the few decent boat dives in Sydney that can be done safely in strong southerly or even south-easterly winds, because Cape Solander and the Kurnell cliffs block the swell. It is open to north-east and east seas, which make it uncomfortable above about 1.5 m. Being near the Botany Bay entrance, low tide can bring dirty water, but McFadyen has had 15 m+ visibility after 50 mm of rain at low tide; an incoming tide is still best.

Summer afternoon north-easterlies are the main nuisance.

Head east from the anchor to the eastern wall (to 23 m) and follow it north for about 7 minutes, return and follow it south for 7 minutes, back to the anchor. Then go west to the sand gutter, follow the kelpier western wall north for five minutes, cross the sand east to the reef and follow it south back to the anchor.

No regular charter – private boat or dive-club (St George Scuba Club) only