The SS Investigator was an iron-hulled screw steamer built in 1882, about 64 m long and 605 tons, working the South Australian coastal trade. On 24 April 1918 she grounded on rocks about 500 m south-west of Wardang Island; the Department for Environment and Water attributes the loss to inaccurate charts of this reef-strewn stretch of Spencer Gulf. She could not be saved and broke up where she lay.

The wreck is very shallow, 3-4 m, and is broken and scattered across reef and sand. Its highlights are unmistakable: both The Dive Shack and SDFSA note that the ship's anchor and propeller are clearly visible, and hull plating, frames and machinery fragments lie around them. The ironwork has become a reef, and fish life is usually prolific – old wives, sweep, magpie perch, leatherjackets and schools of small baitfish, with crabs and octopus in the crevices.

Because it is so shallow, the Investigator is ideal for snorkellers and new divers, and it lets photographers work in bright, natural light. It is, however, on the exposed south-western side of the island, so surge and swell are the limiting factors; on a calm easterly day it is superb. It combines naturally with the nearby Notre Dame d'Arvor and Aagot on the western side, or with the Australian, MacIntyre and Monarch on the southern shore, making a full day of wreck diving on the trail.

Because the site is so shallow, a single cylinder lasts a long time, and snorkellers in the boat party can enjoy it as much as divers. Photographers get the best results around the middle of the day when the sun is high and the ironwork is lit through the clear water.

From Adelaide drive about 190 km (2 hours 15 minutes) via Port Wakefield and Maitland to Port Victoria. Launch at the Port Victoria boat ramp beside the jetty and run west to Wardang Island – the island's nearest shore is about 8 km away and the southern wreck sites about 11 km (20-30 minutes in a small boat). The Port Victoria Maritime Museum and the Department for Environment and Water trail booklet give site details and coordinates.

Wardang Island is Aboriginal land held by the Point Pearce (Narungga) community: diving the wrecks from a boat is fine, but landing on the island requires permission. The Investigator lies about 500 m off the south-western side of the island, roughly 11 km from the ramp (25-30 minutes). Anchor in sand nearby; the site is shallow enough to see the wreckage from the boat on a clear day.

Wardang Island lies 8-11 km off Port Victoria in Spencer Gulf. Its western and southern shores – Aagot, Investigator, Notre Dame d'Arvor, Monarch, Australian and MacIntyre – face the open gulf and are subject to south-westerly swell, surge and wind-driven sand movement, so they need low swell and light winds, ideally easterlies. The eastern and northern sites (Songvaar, Moorara) are more sheltered from the prevailing south-westerlies but exposed to northerly and easterly chop.

The 20-30 minute boat run from Port Victoria becomes uncomfortable above about 15 knots. Summer and autumn mornings are the usual window; winter fronts bring days of south-westerly weather. At 3-4 m the Investigator is strongly affected by surge in any south-westerly swell.

Drop in near the propeller, follow the shaft line and scattered plating forward to the anchor, and explore the reef around the wreckage. Snorkellers can follow the same route from the surface.

No resident operator; included on Adelaide shop and club Wardang weekends and dived by private boats from Port Victoria in summer.