Swimming with Australian sea lions at Hopkins Island is one of Port Lincoln's signature experiences. The Marine Life Society describes the island as a relatively small rock with smooth slabs of stone along sandy beaches and a tiny protected bay, Seal Cove, where sea lions enter the water and come over when divers arrive. Landing is prohibited, but that does not matter: as the boat anchors, the animals slide off the rocks and into the water to investigate.

Australian sea lions are an endangered species found only in South and Western Australia, and they are famously curious. In the clear, shallow water of the cove, juveniles in particular twist and spin around snorkellers, blow bubbles, mouth fins and mimic swimmers' movements – behaviour that has earned them the nickname 'puppy dogs of the sea'. The bay floor is sand and seagrass with granite boulders, and small reef fish and rays are seen alongside the sea lions.

For scuba divers, the island has more to offer. A pinnacle off the south-west tip rises from about 30 m to 4 m, with boulders and numerous caves and a variety of marine life, making a fine deeper dive when conditions allow. The sea lion swim suits everyone who can snorkel, including families, and tours supply wetsuits and gear.

It is often combined with a Neptune Islands shark trip. Best practice is to let the animals come to you and never to touch them, and bull sea lions should be given space. Water temperatures around 14-19°C mean even summer swimmers appreciate the thick wetsuits supplied on tours.

Port Lincoln is about 650 km (7 hours) by road from Adelaide via Port Augusta and the Lincoln Highway, or a 45-50 minute flight (Rex/QantasLink). Sea lion tours leave Lincoln Cove Marina and run south through Boston Bay and Thorny Passage to Hopkins Island (about an hour each way depending on conditions); Calypso Star Charters visits Hopkins, Grindal or Blyth Island depending on weather. Landing on the island is prohibited – the sea lions come into the water when the boat arrives.

Boston Bay and the waters around Port Lincoln are sheltered from Southern Ocean swell by Boston Island and the Lincoln National Park coast, so the town jetties can be dived in most weather; strong south-easterly and easterly winds are what chop them up. The islands of Thorny Passage and the lower Eyre coast are progressively more exposed to south-westerly swell and strong tidal streams, and need swell under about 1.5-2 m and light winds. Winter (May-August) brings frequent cold fronts with big south-westerly swell but also calm, clear spells; summer has more reliable weather but regular afternoon south-easterly sea breezes.

Water is cooler than the gulfs, around 13-15°C in winter and 17-20°C in summer. Tours choose between Hopkins, Grindal and Blyth islands to find the lee on the day.

Snorkel quietly in the shallow bay and let the sea lions approach; stay horizontal and avoid reaching out. Divers can drop to the sand at 3-5 m. On the pinnacle, descend to the boulders at 20-30 m and spiral up the rock through the caves to 4 m.

Calypso Star Charters runs half-day 'Swim with the Sealions' tours (Hopkins, Grindal or Blyth Island) and shark/sea lion combos; the former Adventure Bay Charters sea lion swims are now under Calypso Star. Scuba on the pinnacle is by private boat or arrangement.