Between continents in Iceland's Silfra Cathedral. All photos: Charles Hood Map Diver above the crack in Silfra lagoon Geyser erupts Monkfish Blue lagoon open-air health spa Wolf-fish hides in a hole Divers at Silfra Topside shot of lagoon A plaice Wolf-fish in the open

I have been banned from using the phrase 'gin-clear water' in DIVE. However, on this occasion I must be allowed to describe the waters of Silfra lagoon as transparent as Gordon's finest! Without question, this pure, filtered water is by far the clearest I have ever dived in. We estimated that the horizontal visibility was around 100m, the only limiting factor being that this was to the other side of the lagoon.

The Atlantic rift is the geological dividing line between the continents of Europe and America. It's a huge crack in the earth's surface, which is slowing widening by about two centimetres per year. In the deep waters of the Atlantic Ocean this crack is mainly unseen, but as the fault cuts its way through the centre of Iceland, gigantic gullies are formed. Melted water from Iceland's glaciers is filtered by the porous lava rock, which in turn flows into these gullies. The clear water sparkles when gas occasionally bubbles from below, a result of deep volcanic activity. The Icelandic people call one particular gully 'The Silver Lady' or 'Silfra' as it is known in Icelandic.

Diving Silfra is surreal. It's probably best described as the closest experience to space-walking you are ever likely to get. Due to the extreme clarity, one loses all sense of depth. Indeed, Tómas Knutsson, who is the owner of the local dive centre in the town of Keflavik, has often had people suffering from vertigo when they first enter the water. The reasons for this outstanding clarity are two-fold. First, it is cold. Its temperature varies between 2 and 4ºC all year round. At this temperature nature stands little chance of supporting much aquatic life. Secondly, the water itself is of the purest form. It begins as distilled water when the leading edge of the glacier melts high up on the Hofsjokull mountain. This water then disappears and runs underground, to emerge once again in the Thingvellir national park. On its journey it is constantly filtered by porous lava rock. The water is so pure that it can be drunk without any form of treatment.

There are three sections to the dive - Silfra Hall, the Cathedral and Silfra lagoon. All three can be visited on one dive, depending upon how cold a diver gets. It's not usually your body that gets particularly cold, but your hands. Our experience was that after about half an hour we had to surface to get some sense of feeling back into our fingers. This was achieved using a Thermos flask full of hot water that had been strategically placed by Tómas at the mid-point of the dive. To get to the entry point of the dive we had to to walk over the tundra for about 50m. This was slow going, and for safety reasons we made three trips, carrying a third of our equipment each time.

I was buddied up with underwater photogapher Peter Rowlands, and Tómas was our guide. We had previously decided that I would lead the dive for the first dive, which allowed me to take images of two divers in the frame. On a subsequent dive Peter was to do likewise - a system that worked well to maximise the impact of the shots. When we reached the deepest part of the dive at around 20m, Tómas descended below the apparent bottom and swam through a cave system. As his exhaust bubbles rose from below, they reflected the light from above, lighting up Silfra Hall like a cut-glass chandelier. The ravine then rose sharply to a depth of barely 1m and we had to almost crawl over the shallow rocks to enter the next stage of the dive. On the other side, a spectacular crack appeared. Gigantic rock formations were on either side of us. We had reached the Cathedral, an awe-inspiring demonstration of the earth's incredible power to simply divide two continents. To our left was the geological continent of America, and on our right, Europe.

By now, 30 minutes had elapsed and we made a welcome stop to bring back circulation to our frozen fingers. We exchanged our experiences enthusiastically - surely nothing could top the dive we had just enjoyed? Tómas, who must have witnessed this many times before, briefed me on the next route to take. I had barely put my head under water when I surfaced again, with a shout of expletives to Peter. We had just turned the corner of the Cathedral and entered Silfra lagoon. To call it 'stunning' is an understatement when describing this site. It was only when we looked from the surface to check how far away the other side of the lagoon was (around 100m) that we got a true appreciation of just how clear the water is. To complete the scene, a second crack runs through the lake's bed. We made a total of four dives at this same site sacrificing some of the other scheduled sea dives. This dive ranks in my Top Ten dive sites in the world, and I would even go so far as naming it in my Top Three.

Iceland also has some excellent coastal dives. It is similar to the South Coast of England, with its water temperature at around 5ºC. Sites we visited included Ottarstadir, Keflavik cliffs and Gardur. The marine life is identical to the species found around the British Isles although noticeably more numerous, with plenty of flatfish such as plaice, flounder and brill. Among the rocks are monkfish, lumpsuckers and wolf-fish.

Diving Iceland

Travelling to Iceland is far easier these days. Iceland Express airlines run a daily service from Stansted airport in Essex to Kaflevik (about 50km from the capital Reykjavik). Flights cost from £123 return and the flight time is two hours. The Hotel Kaflevik costs from £90 per night per person and is a few minutes' walk from the dive centre. Diving packages start at £150 and include cylinders and weights. Alternatively, you can hire all your equipment if required. It is possible to dive Silfra over a long weekend.

Surface interval

If you find yourself with a few hours spare, Iceland has some excellent topside attractions. Walkers and hikers will enjoy the sight of erupting geysers and you can also visit the Blue Lagoon open-air health spa, where the geothermically heated water has been found to have healing properties.

Alternatively, a trip on the MS Moby Dick offers the chance to see several species of whales and dolphins.

DIVE would like to thank:

The Dive Centre (Tómas Knutsson)
00 354 897 6696
http://www.dive.is

Iceland Express airlines
0870 8500737
http://www.icelandexpress.com

Hotel Kaflevik
00 354 420 7000
http://www.hotelkeflavik.is

Blue Lagoon
00 354 420 8800
http://www.bluelagoon.is

Whale watching
00 354 421 7777
http://www.dolphin.is