The Iron Pot is a small rocky island at the mouth of the Derwent, crowned by the Iron Pot lighthouse, erected in 1832 and regarded as the oldest operating lighthouse in Australia. The Marine Life Network guide describes it as easily reached from South Arm, in 2-15 m, with a sheltered western side and a more dramatic eastern side. At the southern end near the lighthouse the sea has split away part of the rock to create a small 'island' with a swim-through, while the eroded eastern face has many small caves and crevices in about 12 m, with sponge gardens at the base of the wall.

Leatherjackets, wrasse, school fish and invertebrates are found around the island, and crayfish, although the guide notes numbers are affected by boat traffic and nets. History is visible too: remains of an old winch used to haul supplies to the lighthouse, and the site where the ketch Caledonia was wrecked. The wreck of the river steamer Lintrose lies nearby in very shallow water.

The Iron Pot is one of the best reef dives close to Hobart and a good alternative to the Betsey Island graveyard when conditions there are poor. The swim-through and eastern caves need calm conditions, while the western side is diveable in moderate southerly weather. Visibility varies with the Derwent: clear marine water after a dry spell and a flood tide, dark and murky after floods.

It suits Open Water divers on the sheltered side and more experienced divers on the exposed face.

South Arm is about 35 km (40 minutes) south-east of Hobart: cross the Tasman Bridge, follow the South Arm Highway (B33) through Rokeby and Lauderdale to South Arm. The main boat ramp is at South Arm (Blessington Street/Harbour area) with trailer parking and toilets; Lauderdale (Doran's Road) is an alternative ramp further north. The Iron Pot lies about 3 km south of Cape Direction, an easy 10-15 minute run from the South Arm ramp.

Anchor on the sheltered western side in sand, clear of the reef.

The South Arm peninsula and Iron Pot sit at the junction of the Derwent and Storm Bay. Western shores and the lee sides of the islands are sheltered from easterlies; eastern and southern faces are exposed to southerly swell rolling in from Storm Bay. Strong southerly winds and swell close the exposed sites; northerly and light westerly winds give the best conditions.

Visibility varies widely, from 3 m after Derwent floods to 15 m in clear marine water after a dry spell and a flood tide. Afternoon sea breezes can make the boat ride back choppy. The western side is sheltered; the eastern side is heavily exposed to southerly swell and the southern swim-through is safe only in very calm weather.

In calm weather drop at the southern end near the lighthouse to see the swim-through, then follow the east side at 10-12 m past the small caves and crevices to the sponge gardens at the wall base. In any swell stay on the sheltered western side.

No scheduled operator trips; popular with Hobart club divers and private boats from South Arm.