The Edithburgh Sponge Garden is a little-known boat site in the shallow water between Edithburgh and Troubridge Island. The Marine Life Society of South Australia describes it as shallow sponge beds about 4 miles offshore, slightly north of the midpoint between the town and the island, in around 6 m, with small offshore reefs nearby and a rip at times. Sponge gardens are one of the signature habitats of South Australia's gulfs: where tidal current flushes a sand or low-rock bottom, filter feeders thrive, and the result is a field of sponges in every shape – fingers, vases, fans and encrusting sheets – in red, orange, yellow and purple, interspersed with ascidians, hydroids and bryozoans.

These gardens are home to a rich small fauna: nudibranchs, sea stars, feather stars, cowries, decorator crabs and pipefish, with leatherjackets, cowfish, globefish and small wrasse moving between the sponges. Blue swimmer crabs, cuttlefish and rays use the surrounding sand. Because it is shallow and current-swept, the sponge garden is best dived as a gentle drift, which lets divers cover ground over the beds without fighting the tide.

It is a site for divers who enjoy invertebrate diversity and macro photography rather than big structure. Visibility is variable depending on tide and wind. Documentation is limited and there is no fixed mark, so divers should expect to search with a sounder.

The site pairs well with the Troubridge Island area for experienced boat divers, or as an alternative when Edithburgh jetty is crowded.

Launch at the Edithburgh boat ramp and head east-south-east towards Troubridge Island; the sponge beds lie about 4 nautical miles (7 km) out, slightly north of the half-way point. Allow 15-20 minutes. The area is shallow with small reefs, so watch the depth sounder and approach slowly.

There is no published mark, so expect to search for the beds with a sounder or by drifting with a lookout; leave a tender on board if the tide is running, as a drifting diver can quickly be carried away from an anchored boat. Edithburgh has fuel, air and toilets at the ramp area.

The sponge garden sits in the open mouth of Gulf St Vincent between Edithburgh and Troubridge Shoal, where tidal streams run noticeably – the Marine Life Society warns of a rip at times – so plan for neap tides or slack water and consider drift diving with a boat tender. Easterly and south-easterly winds make the area choppy and cloud the water, while southerly swell wraps around Troubridge Shoal in big weather. Calm days with light westerly or northerly winds are ideal.

Drop in at the northern side of the beds and drift slowly with the tide over the sponge gardens at 5-7 m, with a boat tender following SMBs, or anchor on sand and swim a square pattern around the anchor.

No regular operator; dived by locals and club members with boats from Edithburgh.