The SS Shamrock is one of several colliers lost at Catherine Hill Bay, the small coal port south of Swansea whose name itself comes from a wrecked schooner. Grey Nurse Charters describes her as a 1,427-ton, 78 m vessel built in 1878, lying in a shallow sandy area north of the Catherine Hill Bay coal loader and dived from the beach near the surf club. COAST Magazine records that she struck a rock soon after leaving the wharf in 1903 laden with 2,000 tonnes of Wallarah coal, and that she lies about 45 m from shore.

What divers see depends almost entirely on the sand. Grey Nurse Charters notes that the structure visible varies with sand movement: after heavy seas scour the beach, iron plates, frames and pieces of machinery can be exposed; after long calm spells, much of the wreck may be buried. This makes the Shamrock a shallow exploration dive whose appeal is history and changeability rather than a fixed layout.

Where metal is exposed, fish gather quickly: luderick, bream, whiting and flathead around the wreckage, with mado and silver sweep and the occasional ray or Port Jackson shark on the sand. Encrusting growth on the plates hosts small invertebrates and nudibranchs. Combined with the old coal loader and the remains of the SS Wallarah nearby, the Shamrock gives Catherine Hill Bay a compact heritage trail of the coal trade.

It suits Open Water divers and snorkellers on flat days, and it is worth checking recent reports before visiting in case the sand has hidden it again. As with all historic wrecks in NSW, nothing may be removed.

From the Pacific Motorway or Pacific Highway take the Catherine Hill Bay exit and follow Flowers Drive into the village. Park near the Catherine Hill Bay Surf Life Saving Club; the beach and the old coal loader jetty are a short walk away. Enter from the beach and swim out north of the coal loader to the wreck area, about 45 m from shore according to local histories.

The remains shift with the sand, so check with Grey Nurse Charters or local divers for recent reports before planning a dive.

Catherine Hill Bay faces east to south-east and the beach catches most swell; dive the Shamrock only when swell is under about 1 m and winds are light westerly or northerly. Rough seas shift sand across the wreck - sometimes burying it completely, sometimes exposing more structure - so visibility and what can be seen change from week to week. Visibility is best after several calm days and poor after storms or heavy rain.

Enter from the beach and swim north of the coal loader to the wreck area; search the shallow sand for exposed plates, frames and machinery. Keep dives short if swell is running and exit back on the beach.

Protected historic shipwreck under the NSW Heritage Act.

No scheduled trips; Grey Nurse Charters lists it among its Swansea-area sites and guides occasionally; otherwise dived independently.