Langton Island is one of the islands of the Sir Joseph Banks Group, and the Marine Life Society singles it out for its Australian sea lion colony, noting that the animals will regularly swim with divers in about 2 m. Australian sea lions are endangered and found only in South and Western Australia, with most of the population in South Australian colonies like those of the Sir Joseph Banks Group. They are highly social and curious in the water, and juveniles in particular approach divers and snorkellers closely, twisting, somersaulting and blowing bubbles.

Diving in 2 m means excellent light and long bottom times, and snorkellers can share much of the experience. Unlike the commercial sea lion swims at Hopkins Island off Port Lincoln or Baird Bay on the west coast, there is no regular tour here, so encounters are for private boat owners and occasional charters. That means responsibility for good behaviour falls on the visitors: keep a respectful distance from haul-outs, never land, let the animals initiate contact, and leave if they show stress.

Breeding islands are protected, and sea lion colonies attract white sharks. Langton Island suits snorkellers and relaxed divers who want an uncrowded sea lion encounter and have a boat. Combine it with Spilsby and Stickney islands.

Summer and autumn, when young animals are active and the weather is more settled, are generally the best times to try.

Tumby Bay is about 600 km (6.5 hours) from Adelaide via Port Augusta and the Lincoln Highway, or 50 km north of Port Lincoln (airport). Launch at Tumby Bay and cross into the Sir Joseph Banks Group (about an hour). Langton Island's exact position within the group should be taken from charts; approach the colony slowly, stay in the water off the rocks and do not land – sea lion breeding islands are protected.

The Sir Joseph Banks Group lies in open water in lower Spencer Gulf, 15-30 km off Tumby Bay. The islands give shelter from one direction or another, but the crossing is exposed to wind from all quarters, and strong south-easterly or south-westerly winds make it rough and unsafe for small boats. Tidal streams run between the islands.

Choose settled days with winds under about 15 knots; summer and autumn mornings are most reliable. Visibility is often good (10-20 m) in the clearer water around the outer islands.

Settle quietly in 2 m off the colony and let the sea lions come to you; stay low and still, avoid blocking their path to the water.

No regular operator; private boats and occasional Tumby Bay charters.