Christies Beach Ledges, also called Christies Reef, is a shallow shore dive at the southern end of Christies Beach, beneath Witton Bluff and just north of Port Noarlunga. The Scuba Divers Federation lists Christies Beach among Adelaide's metro shore dives, and the Marine Life Society of SA has documented it for decades, with a 1979 survey describing brown kelp Ecklonia everywhere. The reef is a band of low rocky ledges and boulders in just a few metres of water, carpeted with kelp, Caulerpa, sea lettuce and other algae, and fringed with seagrass beds.

Under the ledges and among the boulders are sponges, anemones, chitons, abalone, sea urchins, starfish and nudibranchs. Fish include magpie perch, moonlighters, brown-spotted wrasse, juvenile blue-spotted goatfish and southern eagle rays. An iNaturalist project for the area had logged more than 80 species by 2019.

The site's claim to fame is the Port Jackson shark aggregation between about November and January. Diving Adelaide describes adults gathering on ledges along the shore and in the shallows at the southern end of Christies Beach during the mating season, with juveniles in the seagrass, and visibility often excellent at that time of year. Divers and snorkellers can see dozens of sharks resting in just a few metres of water.

Being so shallow and easy to reach, Christies Beach suits snorkellers, families, new divers and photographers. Outside shark season it is a pleasant kelp and ledge dive and a quiet alternative to Port Noarlunga. Keep a respectful distance from resting sharks, and leave egg cases where they are.

Drive to Christies Beach (35 minutes south of Adelaide) and follow The Esplanade to its southern end below Witton Bluff, where there is roadside parking. Walk a short distance onto the beach and enter over sand beside the rocks; the reef begins in the shallows and extends north of the bluff. The walk is short and flat.

Port Noarlunga's facilities are a few minutes' drive south.

A shallow, west-facing beach site that needs calm, clear conditions. Light easterly or northerly winds and low swell are ideal; westerly or south-westerly winds or swell over about half a metre create surge and stir up the sand. The summer sea breeze normally arrives around midday.

Visibility is often excellent on calm early-summer days, which coincides with the Port Jackson shark season, but falls after rain when the Onkaparinga River flows.

Enter at the southern end of the beach and swim north along the reef edge at 2-4 m, checking under ledges for Port Jackson sharks in season; turn at half gas and return close inshore over the seagrass for juveniles.

Diving Adelaide – seasonal Port Jackson shark snorkel and dive tours (November-January); SDFSA lists it as a metro shore dive; clubs and Marine Life Society of SA surveys.