The SS Northern Firth was built in 1922 at the Grangemouth Dockyard in Scotland as the SS Willowpark and renamed by 1932. She was a 1,931-gross-ton steel steamer, 280 feet long and 42 feet wide, with a single triple-expansion engine, owned by the North British Shipping Company and chartered to James Patrick and Company. On 21 February 1932 she struck a submerged reef just off Brush Island, south of Bawley Point. A hole was torn in her side and the engine room flooded quickly. Strong north-easterly winds then drove her onto the north-eastern corner of the island. All the crew reached shore safely.

The cargo, valued at £90,000, included shoes, clothing, liquor, beer, glycerine and syrup, and locals helped themselves before a wreck guard arrived. Salvors worked the wreck from 25 February to 10 March 1932, by which time she was breaking up quickly. A Marine Court of Inquiry cleared the second mate because the reef was not on the Admiralty chart.

Today the Northern Firth is a scatter of rusted steel plates and frames on the reef and sand beside the island, with some pieces visible on the island and the mainland shore. The one substantial feature is a huge boiler, still lying as it would in the ship, which is wide enough for divers to swim through side by side. McFadyen dived it in 1993 and then failed to find it again in 1995 and 1996. The Marine Life Network gives the boiler depth as 26 m, while other accounts suggest much of the wreckage is shallower. Surrounding reef carries kelp, sponges and schools of reef fish. Brush Island is in the Batemans Marine Park and is also grey nurse shark habitat. It is a long trip for a scattered wreck, so the site mainly suits divers interested in wrecks and history.

Boat access only. From Ulladulla Harbour the boat runs about 20 km south past Bawley Point to Brush Island, which sits just off Murramarang Beach; allow about 45 minutes. Batemans Bay boats (Hanging Rock ramp) can also reach it, heading north past Durras.

McFadyen's GPS mark was supplied by Derek Hickey in 2010, and he notes that most of the wreckage seems to be about 20 m west of the mark. Anchor clear of the wreckage on sand or rubble.

Brush Island is exposed to north-east and south-east swell, and it was a north-easterly that drove the ship onto the island. The 45-minute run from Ulladulla means you need a settled forecast: less than about 1.5 m of swell and light westerlies or north-westerlies. Southerly changes arrive quickly on this coast; watch the forecast and be prepared to head home.

The shallow reef south-east and east of the island breaks in bigger swell. Visibility is lower after heavy rain from nearby lagoons and creeks.

Descend near the mark and search about 20 m west for the boiler, the most substantial piece of wreckage. Swim through the boiler if your buddy team is comfortable, then follow the scatter of plates and frames towards the island. Keep an eye on depth and gas, and return to the anchor line for the ascent.

Wreck is a historic shipwreck (over 75 years old) protected under the Underwater Cultural Heritage Act 2018: look, do not take.

Dive Adventures Ulladulla lists Brush Island (wreck dives, max 25 m+, experience required) and runs it occasionally when seas allow. Otherwise private boats from Ulladulla or Batemans Bay and visiting clubs.