Our small wooden vessel rocked gently on the water, revealing little of the wild currents sweeping over the coral reefs below. On the signal of our experienced dive guide Arun, we rolled off the boat and descended into the cobalt ocean.
Flying with the fast water flow, we raced past a forest of brightly coloured giant gorgonian fans and traversed through a labyrinth of large volcanic boulders.
Every few minutes we clung to these rocks to watch tiny creatures taking shelter in the coral reef, and to stare into the blue. It wasn't long before a blacktip reef shark appeared. The sleek figure moved closer, up to 10m away, before disappearing into the depths. It was a thrilling hour of high-energy diving.
I was on the northernmost edge of Pulau Weh, a remote jungle island off Sumatra. Once part of the Sumatran mainland, Pulau Weh became separated during the last volcanic eruption more than a million years ago. It is surrounded by healthy and vibrant coral reefs, and its waters harbour a diverse mix of Indo-Pacific marine life.
These exposed, nutrient-rich waters attract ocean giants. Sunfish, manta rays and the largest of all fish, the whale shark. Thresher sharks have also been sighted by divers passing over deep volcanic channels, as has the extremely rare and elusive megamouth shark.
Weighing up to a tonne and growing to five metres in length, this deep-dwelling shark was discovered only in 1976. Few megamouths have been seen since - only 42 sightings recorded to date worldwide.
In Pulau Weh, however, the prehistoric-looking creature has been spotted twice by divers in the past four years. One washed ashore on the Gapang Beach house reef in 2004, another swam by a shipwreck at 50m the following year.
After five days, I realised I was not set to join the elite club of megamouth spotters, but had thrilling encounters with turtles, curious reef sharks and huge Napoleon wrasse.
The diving here offers something for all skill levels, with reef walls, deep and shallow shipwrecks, sloping house reefs, underwater hot springs and excellent drift dives. A giant stride from the dive centre, the house reef is teeming with macro life, including ghost pipefish, seahorses and psychedelic nudibranchs (sea slugs).
I was particularly struck by the impact of Sharia law. I was told that Sharia had all but eliminated illegal fishing here - a rare situation in southeast Asian waters. Most of the dive sites are in marine protected areas, where fishing is forbidden, and illegal fishing operations are frightened by the prospect of heavy punishment handed out by Sharia courts.
Despite its wealth of underwater attractions, Pulah Weh is not an instantly familiar destination to divers. Until recently, both political and environmental turmoil had deterred the average diver tourist from making the journey from the city of Banda Aceh on the mainland.
Now you can arrange in advance to collect a visa in Banda Aceh, flying there via Kuala Lumpur.
Banda Aceh was also the closest major city to the epicentre of the earthquake which triggered the Boxing Day tsunami in 2004 in which around 130,000 Indonesians died.
Miraculously, no one at Lumba Lumba or the surrounding village was killed. Buildings were swept away, but the main structure of the dive centre stood firm. The steely determination of the Dutch owners, Ton Egbers and Marjan van der Burg, who set up the centre in 1998 after diving and backpacking through the region, has seen dive tourism pull through difficult times.
Lumba Lumba is very much part of the Pulau Weh community. Locals have been trained for free as dive masters and now work for the centre. Beach houses and classrooms were built and serviced by local hands, using generations-old techniques, and only natural materials found on the island.
Visiting divers are a valuable source of income here, and it's sure to attract eco-friendly and socially conscious travellers, looking for raw adventure where few have finned before.
For more information, visit www.divesafariasia.co.uk and Lumba Lumba Dive Centre at www.lumbalumba.com