The Steel Barge S4 is a minor wreck listed in the Fraser Coast diving guide: a steel barge lying in about 12 m north of Big Woody Island, described simply as 'a shorter dive'. No history of the vessel or detail of its condition is published, and it does not appear on current operator site lists.

As with other structures in Hervey Bay, a steel barge on sand in shallow water will act as a fish-attracting reef. Expect encrusting soft corals, sponges and ascidians on the hull, with scorpionfish and stonefish tucked into the growth, and bream, cod and baitfish around it. The shallow depth means bottom time is not a limitation, but the small size of a single barge means there is not much to see once you have circled it.

Diving conditions are those of the bay: best at high-water slack, visibility often only 3-5 m, and more after a spell of calm winter weather. The site lies near the Great Sandy Strait channel, so watch for boat traffic.

It is best treated as an optional second dive for divers with their own boat who already know the area, rather than a destination. Visitors will get more from Roy Rufus, Moon Ledge or the ex-HMAS Tobruk, all serviced by Hervey Bay Dive Centre. If you do visit, confirm the barge is still intact and in place with local divers first: small steel structures in the strait can shift, break up or be buried by moving sand over the years.

Hervey Bay's boat dives leave from Urangan Boat Harbour (Great Sandy Straits Marina / Boat Club Marina, Buccaneer Drive, Urangan), at the eastern end of Hervey Bay's Esplanade about 10 minutes' drive from Pialba; there is free parking at the marina and a public boat ramp in the harbour. Hervey Bay Dive Centre runs its local wreck and reef trips from here. The barge lies north of Big Woody Island, a short run of roughly 15-20 minutes from Urangan.

No public mark is published; obtain it locally and drop a shot or anchor in sand beside the wreck.

Hervey Bay lies in the lee of K'gari, so ocean swell is rarely a problem; the limits are wind, tide and visibility. South-east trades over about 15-20 knots kick up a steep, short chop across the bay, and strong northerlies do the same in summer. Tides in the Great Sandy Strait run hard, so dives are timed for high-water slack – the Roy Rufus reef is dived only around high tide – and neap tides give the calmest water and best visibility.

Visibility is modest, typically 5 m and rarely above 10 m, and drops further after rain when the Mary River and creeks discharge into the bay (December-March). Winter (June-October) is generally calmer and clearer, and coincides with humpback whale season.

Descend to the barge at about 12 m, circle it and inspect the growth. It is a short dive – combine it with a longer site such as Roy Rufus. Ascend on the line at slack water.

No regular operator documented – private boat; ask Hervey Bay Dive Centre.