A swim in the quiet storm

It was like being in the rinse cycle of a washing machine. Forty feet under water, we swam round a bend of the great wall of coral and suddenly collided with a powerful whoosh of current. Under such circumstances there's little you can do but go with the flow. And observe how the locals are coping. The bigger fish had been able to fight their way through to stiller, lower depths but the small fry, forced to abandon their snacking ground, were swept along with us, little dorsal fins quivering in the sea gale. It was gratifying to feel that we were all in this together. A few minutes later the tumbled gang - assorted angelfish, fusiliers, mini wrasses and scuba divers - had managed to twist free of the water force, no harm done.

In calmer quarters, we all resumed our varied activities: the fish got down to the serious business of nibbling on passing plankton and browsing through soft coral, the divers carried on gliding through the now serene seascape, hedonists on an aquatic sightseeing tour. There's no sense of "been there, done that" with scuba diving. It's always an adventure. You get a buzz from the fact that this is a potentially hazardous sport, from the sense of magic as you sink into a gloriously alien world of sublimely coloured plants and fish - and from the challenge of being caught in a strong current.

The adventure is perhaps all the greater in Indonesia, where the trail for coral and fish also leads you to remote regions - volcanic landscapes of lush beauty, deserted tropical islands, people of appealingly different customs and cultures. This vast archipelago stretches further than the distance from London to Moscow and contains about a sixth of the world's coral reefs. The fragile underwater environment here is relatively unexplored and unvisited: it's barely 10 years since the first commercial dive operations were started in the area.

There are, however, some disadvantages to this - facilities tend to be basic and safety standards alarmingly relaxed. One of the best and safest places for coral gazing is off the top of Sulawesi, north-east of Java. In terms of landmass, the island is the size of England and Scotland, although its bizarre shape makes it seem bigger: on the map, Sulawesi looks a bit like a slouching starfish. Manado, a bustling little coastal town on the extreme edge of the upper arm, is just a short boat trip away from an area of spectacular sea scenery. As yet, only a few dive companies operate here. The outfit I signed up with promised "fully trained guides, not just somebody who knows how to blow bubbles", a reassurance with worrying undertones.

But, sudden currents aside, it turned out that there wasn't much cause for anxiety as the group of novice Indonesian divers I joined was patiently shepherded through the deep. We spent four days, in perfect conditions, exploring the crystal-clear waters around the volcanic islet of Bunaken. Here, a stunning wall of coral drops sheer down, looking as if it falls into an infinity of blue.

Quite apart from such panoramic drama, the attraction of going to the wall lies in the enormously rich variety of marine life it supports: beds of soft sea anemones, great barrel organs of sponges, battalions of barracuda, horizontal trumpet fish, fleets of black triggerfish, and more. If you're lucky you might catch sight of sinister-looking moray eels, tiny seahorses and inflated pufferfish hoping they've swelled themselves so big as to be inedible.

Kitted up with weight belt and scuba tank you feel as ungainly as an overfed elephant as you prepare to plunge into the water to meet these creatures. It seems a minor miracle of physics that once you start your descent you acquire a weightlessness in defiance of these encumbrances.

Agility and grace are rather more difficult to achieve. Yet as you clumsily bubble into the wateryworld, the schools of little reef fish you pass look remarkably unstartled. Unlike animals on land, many of the small underwater species do not beat a hasty retreat at the sight of a human. They simply hang around like suspended confetti - presumably they have the second sense to know that you're a cumbersome oddity rather than a predator.

This is rarely the case with larger sea life. A shy turtle, scarpering into the salty distance, was the first creature I saw as I plummeted into the Bunaken underworld (judging by the amount of tortoiseshell you can still find for sale in Indonesia, perhaps it had good reason to be nervous). At a depth of about 70ft, a massive couple of spotted eagle stingray lolloped swiftly away from us, looking rather like marine UFOs.

A little later we peered down on a prowling reef shark which sped out of sight once it became aware of our presence. We were lucky.

A shark sighting is generally something to get excited about: you can't help but be impressed by the sheer power and size of these big fish. And unless you go shark baiting, or appear to be a creature in distress (as you do swimming on the surface of the water), you are, apparently, unlikely to become lunch for these primitive bundles of aggression.

"I think it's all those bubbles. Sharks can't stand them" one of my fellow divers later commented. He and his wife were cheerful yuppies from the capital, Jakarta, and were diving on honeymoon. "Not what Indonesians normally do, but we've both become addicted." And they wanted photographs of the event. We duly obliged with an underwater camera, taking pictures of them, several group shots, and a few photographs of passing fish for good measure. Posing at a depth of 50ft is not something they cover at dive school, so we acquired new skills in lining up, keeping still and attempting to smile with a regulator-filled mouth.

Dipping into reference books to identify the fish I'd seen, I thought that the coral reef was, inadvertently, a pretty kinky place for a honeymoon. The sex life of many of the fish is bizarre. The valiant little clown fish which live in the tentacles of sea anemones are a case in point.

These tiny orange-and-white fellows will defend their patch vigorously, aggressively darting out at intruders, including passing divers. They mature as males but a few will then become female and pair off with a dominant male. The couple take up residence in an anemone along with a group of smaller, younger males. Should the female die, her partner will do a swift sex change and take one of the young males as her mate.

Many wrasses, groupers and parrotfish have similar hermaphroditic tendencies - not that you see such gender gymnastics taking place in front of your eyes, but the knowledge of it adds to the wonder of the underwater world.

Life on dry land might seem a bit dull by comparison, but northern Sulawesi compensates with a generous sprinkling of active volcanoes (Mt Soputan last erupted in 1989), a few sulphurous lakes and a crowd of good-time people who seem to spend every available opportunity singing and playing guitars. The Minahasa are renowned for their exuberance by other Indonesians - and also for their taste in food: in the sprawling market at Manado they do a brisk trade in rat, bat and dog meat.

And business, generally, is good. This is, by Indonesian standards, a rich area, supported by coconut, nutmeg and clove crops. Currently, there's some concern about the bottoming out of clove prices. "But now we've got a new tourist industry," my dive guide enthused. Indeed, investors are moving in: Novotel, for one, has seen fit to sink money into the area with a large hotel under construction in Manado.

It's difficult not to share the prevailing optimism of the locals and to hope that tourism will have huge benefits. Visitors come here principally to see the coral and its attendant wildlife, which means that the reefs must be preserved. And to this end the fragile underwater world around Bunaken island has already become protected as a national marine reserve.

How to get there: Although Manado has an international airport, there are no direct flights from the UK. The most convenient route is via Jakarta or Bali. Harriet O'Brien flew to Jakarta with Qantas; the return trip cost pounds 586 through Quest Worldwide (0181-547 3322). The Indonesian airline Garuda International (0171-486 3011) is currently offering an airpass around the archipelago for pounds 243. This lasts 60 days and allows you a maximum number of seven flights. British visitors to Indonesia do not require visas.

When to go: Diving conditions are best in Sulawesi between April and October. The rainy season generally starts in November, when visibility becomes poor and access to the reefs around Bunaken difficult.

Whom to trust: Harriet O'Brien paid pounds 40 for two dives per day organised by the Barracuda Diving Resort at Molas, Manado (tel 00 62 43154288, although communication is better by fax on 00 62 43164848). The price includes boat trips, lunch, hire of weight belt and professional guidance. Diving in Indonesia is in its infancy and not all operators offer qualified instruction or adequate equipment for hire. If possible take your own wet suit and regulator.

Where to stay: The Barracuda Diving Resort has comfortable accommodation: an all-in package for room (without air conditioning) and two dives per day costs from pounds 50. Other hotels in Manado include the Hotel New Queen (00 62 431 65979) which charges from pounds 10 a night.

What to read: Underwater Indonesia is published by Periplus, price pounds 9.95