The islands of Vavau, in the South Pacific, teem with marine life, and are undeveloped to the point of quaintness. by Pete Atkinson

Vavau, in the Tonga islands of the South Pacific, is quaint. This is a sympathetic word to describe an island group so undeveloped that the main town only got street lights last year. And it was such a big event that the King came to switch them on. So quaint that the dive operators - both of them - often dont have oxygen because the hospital runs out and borrows it in an emergency. Its the kind of place you expect to find mail for Capt J. Cook which the post office has yet to forward.

The 60 mostly uninhabited islands which comprise the group lie within an area only 20 miles square. The great diving in Vavau is a direct result of its astonishing volcanic topography. Tonga is part of a great chain of volcanic activity stretching south through the Kermadecs to White Island in New Zealand. Tonga is far enough west to have much of the species diversity of Fiji, with plentiful sea fans and soft corals. The dive operators can almost guarantee white tip reef sharks at some sites, and if you speak sweetly in the right ears you may get out to the Fish Aggregation Devices (FAD) anchored in deep water offshore, where you usually see silky sharks and sometimes dorado and oceanic white tips.

There are no rivers, and the visibility on a really bad day is 20m. Although November to April is hurricane season, the summer is a lovely time to be in Vavau. The water is warmer and everything is happening; the fish and invertebrates are breeding, the plankton blooming. The trade winds, which can be frenetic in winter, are more relaxed. For humpbacks though, July to the end of October is the best time. The water is cool then: about 26C. In winter 40m visibility is common.

The main town of Neiafu has changed very little in the last ten years. Its main road is barely sealed, and becomes a muddy torrent when it rains. Its waterfront is lined by a number of old wooden buildings, the oldest of which is the Vavau Club. It used to have a simple method of dealing with rubbish; bottles, cans and paper plates were hurled out of the window onto the slope below. From time to time this tip was cleared up. The administrative buildings include the old wooden post office. Nearby is the Telecom building, where you can phone 24 hours a day, even on Sundays, and a small library. So Neiafu has all the hallmarks of civilisation.

Right in Neiafu harbour is an excellent wreck. In the 1920s the ore carrier Clan McWilliam was alongside the wharf when it caught fire. The captain and engineer motored the ship across the harbour, intending to beach her in shallow water. They never made it. The ship lies upright in about 35m of water. Although the visibility in the harbour is seldom more than 20m, due to a profusion of plankton, the wreck is richly colonised by hard and soft corals, and is the haunt of large numbers of fish.

Dropping down the heavy mooring rope adorned with sponges and bright ascidians, the wreck looms out of the dark. The water is thick with ctenophores and other zooplankton, which brush against my cheeks like snowflakes, appearing from a distance like stars in a Star Trek movie. I settle among the Halimeda algae and sediment on the aft deck at 24m. There are bubble corals nearby, and I find the transparent purple and white palaemonid shrimps usually associated with them. When I poke my camera housing towards them they lift off, rocking back and forth in some kind of display beyond my ken. But out in the open they are vulnerable to attack by lizard fish, which launch themselves faster than I can see.

The wrecks ironwork is covered with Lobophyllia corals which, like the loose change of Fungia corals scattered on deck, fluoresce with colours which seem foreign here. I photograph what appears to be orange Fungia next to a green sponge; my pictures, when they return, show green Fungia and an orange sponge. A torch is a handy thing even during the day to reveal a kind of truth in the blue-filtered gloom. There are encrusted bivalves with serrated shells, winged mussels and heavy Spondylus bivalves, with smooth shell margins and mantle patterns like exotic wallpaper.

The clownfish anemones are huge, with tentacles as thick as pencils. Everywhere are green colonies of Goniopora polyps, like clumps of daisies. Passing over the ships holds I look down upon sedate shoals of crescent-tailed bigeyes, their reflective tapetums looking like silver cataracts. The shoals of the batfish Platax orbicularis are coy. I make my way the 90m to the foredeck, passing busy shoals of fish like a cross between a mackerel and a basking shark: all mouth, hoovering plankton. The foredeck is small, but I find a vase sponge with wispy cobwebs uplifted by the continuous current from the osculum.

There are Thor shrimps too, but although they are next to a bubble coral they refuse to dance over the balloons; it is not their territory. The second mooring is chained to the foredeck, so I ascend slowly, leaving behind only some disturbed sediment and a few regrets about the pictures I did not take.

One other wreck is at the south end of the island of Hunga, at the base of a rock called Tefitomaka. At the surface, shoals of two-spot darts sway in the surge. Fifteen metres below lie the remains of an old wreck, said to be that of a blackbirder. We heard rumours that someone had once discovered a gold coin among the encrusted debris. The wreck site is so old and concreted you would need explosives to find anything. There are a number of bronze and copper pins and two huge anchors. What struck me most were the brilliantly-coloured blue tangs, surgeonfish which dont want to be photographed, and the soft corals. The rock is washed by ocean water and patrolled by schools of big-eye jacks, the males of each pair in dark breeding colouration.

Probably the best dive is on the west of Hunga, and is called Hunga Magic. Imagine a hooked promontory jutting from the cliffs, but submerged 10m. The walls are sheer to 40m. You can rest at the pointed tip, facing the current, which comes billowing up from below as it hits the wall. The water is often crystal clear. You can see pelagics ghosting by, and below, the sandy plain sown with garden eels. There are huge fans on the cliff, and the top is covered with soft corals of every hue, sprinkled with fairy basslets. Fairy basslets are challenging and beautiful subjects to photograph, and disappear into the coral at the slightest provocation. They are sequential hermaphrodites, the male guarding a harem of females. If the male dies, the dominant female changes into a male and takes over the harem.

Between Hunga and the main island of Vavau are a few small cliff-bound islands which offer spectacular diving within a small area. Fotula is one of these, a pinnacle 26m high above water, and another 40m sheer below. Maybe Fotula is my favourite dive; I had no doubt about it before I dived Hunga Magic.

I anchored the dinghy precariously on the steep slope, and drifted down its barren, scoured surface of contracted soft corals and dancing fairy basslets (among which I was surprised to see Pseudanthias cooperi) to a huge boulder at 25m with two tunnels beneath. Passing a Napoleon wrasse and a large double-headed parrotfish I finned up the slope to the west, reaching an arete. It was sharp and sheer. The east-going ebb was buffeting ocean water against the cliff, and I could see for ever. Like a hang-glider I dropped over the edge and down into the blue. Concealed by white and red soft corals, sea fans, sea whips and trees of black coral was the entrance to a tunnel. Taking care to avoid their delicate branches I eased inside. In my narcotised state I was delighted to see long-nosed hawkfish on the black coral: the first I had seen east of Fiji. At the far end of the tunnel were more black coral trees and plate Acropora in which juvenile blue tangs were hiding like Chromis. Decompressing in the lee with the remnants of post-dive euphoria, I found a blue jellyfish and blasted off the film.

Others of these small islands have huge caves, frequently the resting place of white tip reef sharks. Grey reef sharks are also seen here. Outside the east cave at Tuungisika the reef is covered with large sea fans, like the Dendronephthya soft corals, common in Melanesia but rare in Polynesia.

The closest anchorage to these islands is a small sandy shelf at Luamoko, an island with the topography of a double-decker bus sticking out of the ocean. The top is thickly wooded with palms and rain forest. On the south end of Luamoko I was delighted to find some Lord Howe or Painted anthias (Pseudanthias pictilus), a species I had not seen before. Just west of Luamoko, beneath the vertical coast of Nua Papu, is Mariners Cave, entered through a large underwater tunnel. Once we had found the dark shadow which marks the entrance on an otherwise featureless cliff, it was quite easy to snorkel through into the cave. Inside there is a large air chamber. The most remarkable thing about the cave is this: when the swell comes in, the air inside is compressed; when it recedes, the pressure drops enough for fog to condense from the moist air, instantly. So the fog comes and goes with each swell. The cave has another access tunnel at 20m.

Many shades of Christianity are represented in Tonga, the most conspicuous of which is the Church of Jesus Christ of Latter-Day Saints. In stark contrast to the tatty, comfortable towns, the Mormon churches are immaculate, surrounded by sterile and manicured compounds, and what appear to be newly-painted buildings. It is pervasive. Even Swallows Cave is not immune. Its walls are covered with graffiti from Elder So-and-So, reaching the parts that other religions dont reach.

Some of the best coral in Vavau is not far from Swallows Cave, at Mala and Ava. One obvious aspect of the greater species diversity in Tonga compared with French Polynesia is the profusion of feather stars. At night they dominate the cliffs. One night I dived the north cliff of Ava, an island about a mile west of Port Maurelle, on the larger island of Kapa. The coast of Ava is vertical to 25m. The cliff has a profusion of coral near the surface; deeper, it is riddled with caves haunted by bioluminescent flashlight fish. By day the cliff is clouded with fish. Among them are the beautifully delicate hawk anthias, Serranocirrhitus latus. On the rock surfaces are calcareous red algae, like smears of yellow and red oils on an artists palette.

A mile south of Port Maurelle is an anchorage between Kapa and the uninhabited island of Nuku. The current flows swiftly between them, and at night dark red basket stars creep out and unfurl their archaic arms to the blizzard of plankton. Darkness brought a profusion of molluscs from the sand and echinoderms and crustaceans from the coral, including a bizarre Dromiid crab with a huge sponge on its back. All I could see was a walking sponge larger than a saucer. I tipped it over and almost disrobed a crab. Dromiids are keen to retain their extravagant hats, which they hold down with the last two pairs of legs. If they lose the cap they find a new sponge and trim it to fit.

There are few fish at night. The parrotfish hide from olfactory predators such as morays in their diaphanous mucus cocoons; other fish, with darkened colours, lie hidden in the coral caves. In waist-deep water I found three stonefish, incredibly well camouflaged. I have seen a lot of stones that looked more like fish than these did. Synanceia verrucosa is probably the most venomous fish of all.

There are few pristine places left in the world, and Vavau is not one of them. Yet its lack of development, combined with its ample beauty, are assets which will increase in value as other parts of the world are inexorably seduced by shopping malls and fast food.

  • You can now book a trip which takes you to Taveuni, in Fiji, and on by a direct flight to Vavau.
  • The main dive operator is Dolphin Pacific Diving, PO Box 104, Neiafu, Vavau, Tonga, South Pacific. Fax: 00 676 70292.