Seal Cove is the signature seal encounter at Althorpe Island. The Marine Life Society describes it as a fairly narrow cove with a huge seal population – more than 150 animals – that are playful and used to divers, sometimes letting divers pat them, and calls it a great dive to finish off a cylinder. It also mentions two of the biggest and friendliest western blue groper in the area.

Visitor information lists gropers, boarfish, rays and crayfish alongside the colony. The seals here are principally long-nosed (New Zealand) fur seals, with Australian sea lions also present around the Althorpes. In the water they twist and dive around divers, blowing bubbles and mouthing fins, and the shallow, sheltered cove means divers can simply settle on the bottom at 8-12 m and watch.

The cove walls carry kelp and sponges, and the bottom holds boarfish, rays and crayfish. Modern practice is to let the animals approach rather than touching them, and to avoid disturbing haul-outs. White sharks are drawn to seal colonies in South Australia, so divers should stay aware and keep dives compact.

Because it requires the crossing to Althorpe, Seal Cove is an occasional expedition site. When conditions allow, it is one of the most memorable marine mammal dives in the state. Snorkellers can also enjoy the seals from the surface on a calm day, although the animals are most playful when divers settle quietly on the bottom.

Summer and early autumn, when pups born on the island are learning to swim, are especially lively. Keep dives relaxed, avoid chasing animals, and leave the cove if seals show signs of stress, such as bulls barking and charging.

From Adelaide drive about 300 km (3.5 hours) via Port Wakefield, Minlaton and Warooka to Marion Bay; Dhilba Guuranda-Innes National Park begins just west of the township (vehicle entry fee, pay online or at the Stenhouse Bay visitor centre). Launch at Marion Bay and cross about 20 km south-west to Althorpe Island (40-50 minutes). The cove is on the island's shoreline; skippers with local knowledge will find it.

Do not land – the island is a conservation park with restricted landing.

The southern tip of Yorke Peninsula faces the open Southern Ocean and Investigator Strait, so south-westerly and southerly swell is the controlling factor: most exposed sites need swell under about 1.5 m and are best after several days of northerly or north-easterly winds, which blow offshore along this coast. Winter cold fronts bring big south-westerly swell and strong winds and can close the area for days. Summer afternoon south-easterly sea breezes make boat runs rough, so launch early.

Visibility is typically 10-20 m in settled conditions but drops sharply with swell-driven surge. The cove itself is relatively protected once reached, but the crossing to Althorpe dictates whether it can be dived.

Descend at the cove mouth, move slowly into the cove at 8-12 m and let the seals come to you; stay low, avoid blocking their exit and keep clear of haul-outs. A good dive to finish a cylinder.

No regular operator; Adelaide club expeditions and private boats visiting Althorpe Island. Often used as the last dive of the day.