It has partnered with two resorts on private islands at opposite ends of Maratua Atoll, where it reckons the best diving to be, to offer tailored itineraries.

Both resorts have day-trip access to sites including manta ray hot-spot Sangakali, and Kakabun, with its rare inland lake full of stingless jellyfish.

The 20-room Nabucco Island Resort sits at the mouth of the lagoon, and thousands of barracuda, sharks, trevally, “excellent macro life and healthy colourful corals” at  nearby sites are reported.

Nunukan Resort, a half-hour boat-ride away, has a 2.5-mile house reef and turtles, eagle rays and leopard, nurse and blacktip reef sharks can be seen, along with large numbers of fish and critters, says DSA, which rates the diving “amongst the best we have seen”.

For £1590 DSA offers a package including return transfers from Maratua, seven nights’ sea view accommodation with half-board at Nabucco, 10 boat-dives, one day-trip to Sangalaki and Kakaban, return transfers from Balikpapan airport to Samboja Lodge, and two nights’ B&B to visit Orangutan Islands & Sun Bear Sanctuary. All flights cost extra.