If you have ever dived the Mediterranean and wondered where the fish life has gone, I can now tell you! It is all around the Medas Islands, off Estartit, at the northern end of Spain's Costa Brava, which is playing host to hundreds of divers each week who have latched on to this outstanding area.

Less than a mile out of the harbour, the Medas Islands comprise two main islands - Meda Gran and Meda Petita - with numerous large outlying rocks and pinnacles that have been carved out by erosion and the action of the sea. They are the seaward remnants of the limestone massif that rises behind and dominates Estartit.

The islands are not particularly high, but the action of the sea has eroded all but the western side, and under water the cliffs plunge away steeply to 50m and more. Limestone is, of course, a relatively soft rock, and the area is also well faulted. This has allowed the formation of many tunnels, archways and complete cave systems, the most spectacular of which goes through Meda Petita from one side of the island to the other. This is known as the Dolphin Cave (cavern would be more appropriate) and a small, bronze statue of a dolphin has been erected at its southern entrance. When I say this is a spectacular cave, I do not use the word lightly: it is huge, and makes Tyes Tunnel on St Abbs Head look like something out of Playtime with Noddy. From the entrance at the north end, it runs more or less level through the island at a maximum depth of 17m for a distance of about 50m, steadily getting broader and higher as it reaches the several entrances at the much bigger south end. You could probably drive two double-deck buses through side by side, with room to spare! There is never a feeling that you might not find your way out, because you are only a few fin strokes into the system when your eyes adjust to the gloom and you can make out blue at the other end. There are also some smaller "windows" and some perfectly circular, vertical chimneys, which emerge somewhere on the island above. These provide a little extra light, but it is still pretty gloomy in the centre of the cave, and common sense dictates that a torch is carried. I am no great fan of going into holes and caves, but I have to say that unless you are possessed of a real phobia about being enclosed, the Dolphin Cave is a relatively easy dive, and one that even the most jaded will find exhilarating.

Apart from their unusual underwater geography, it has been known for many years that these islands are biologically rather special in Mediterranean terms, with conditions that favour the development of marine life. The River Ter enters the sea just a few miles to the south, enriching the water with organic material. A combination of winds and currents from the north causes an upwelling of deeper water around the islands which brings more nutrients from as far away as the River Rhone in southern France. All of this creates a fertile cocktail on which many organisms thrive.

Some years ago, a far-sighted Catalan Government (the regional government for this area) took all this on board, and realised what a treasure it had on its doorstep. With good management it could be rejuvenated after years of mistreatment and preserved for the benefit of diving tourists and the local economy. So in 1983, it passed the first of a series of laws declaring the islands a marine reserve. What an excellent decision that has proved to be.

Although the caves are a major attraction, they are not the whole story. Excellent dive sites abound, particularly where the cliffs go plunging almost straight down. But the icing on the cake, thanks to the protection afforded by the reserve, is the marine life. Many of the rock walls from 20m down are festooned with beautifully coloured sea fans; red, yellow, purple and even combinations of these colours. They make a stunning sight. And after years of unrestrained exploitation by commercial divers, semi-precious red coral is again developing well on many of the underhangs that it appears to favour.

Encrusting life on the rocks is amazing, and anybody who is into macro photography will go wild with delight. But what astounded me above all were the fish. I have seen nothing like it anywhere else in the Mediterranean: for sheer quantity, these islands remind me of the Red Sea. This was a revelation, because when I last dived this site in 1967, Estartit depended as much on fishing as on tourism, and there was a large and active fleet that fished extensively round the islands. The spearfishing craze was at its height, and few devotees paid any attention to the local legislation outlawing the use of spearguns with diving equipment. Decent-sized fish were a rarity, and those that remained were extremely wary. Now there are tame groupers on every dive; shoals of sardines and anchovies attract pelagic predators such as jacks, bonito, bass and barracuda, and there are so many different sorts of bream circling around in front of your mask that they restrict the view.

The reserve appears well-organised, with a comprehensive set of sensible, legally enforceable rules backed by a policing system. It enjoys complete local support, even among fishermen, who are excluded from operating within 200m of the islands at the reserve's closest point, and a much greater distance if they wish to trawl. Although they were initially reluctant, the presence of so many fish around the islands has benefited their catches generally.

Permanent mooring buoys are provided at all diving sites, and these are colour-coded to denote whether they are for use by local dive schools or by private boats. There are five diving operations in Estartit, and all work to a monthly integrated timetable, which rotates them in turn around the various sites. There are even fallback timetables that come into operation when the the two most common strong winds blow - the Tramontana (NNW) and the Garbi (SSW). Private boats have to book a buoy with the reserve office, and all these sensible arrangements preclude overcrowding at any location. Transgression of the rules is punished severely: confiscation of all equipment has been the minimum penalty on the few occasions when somebody has tried some illegal fishing.

The reserve is successful; to prove it you need only to dive from the rugged cliffs running north from Estartit, which enjoy no protection at all. The contrast is dramatic, particularly in terms of a much-reduced and less-approachable fish population. The reserve is financed through a charge by the authorities of 1.60 per dive. Some of this is allocated to support the decompression facilities for the whole of the Costa Brava, which are located centrally at Palamos, about 30 miles south of Estartit. While any charge is a bind, when tangible results are so apparent, I do not object.
 
We chose to dive with Unisub, a British-owned operation and BSAC school established in 1965 by Tony Murray and staffed by an  international team. Two 12m boats are operated, each with inflatables as tenders and all the usual safety equipment that you would expect on a modern dive boat. I hate being herded around in a big group when diving (which seems to be the norm at many German operations), and was delighted to find that after we had presented our qualifications, we were allowed to do our own thing from the moment we hit the water. Surprisingly, however, there was no briefing about what to do and not do in a marine reserve. Costs are around £15 per dive, including tanks (10, 12 or 15 litres), weights, boat, VAT and reserve entry fee. The other six centres have similar facilities and charges, and all offer a variety of package deals for multiple dives.

The area can be quite windy at times in summer, but there is rarely a time when a lee shore is not available. I was disappointed to find visibility of only 10-12m during October, with lots of particles in suspension, but this was possibly due to the fact that the River Ter was flowing quite rapidly at the time. It is no more than a trickle in the summer, which is the period of best visibility. While a 3mm wetsuit might be satisfactory at a push in July, it was a bone-chilling mistake in October, when the surface temperature was around 18C. The loan by Unisub (free!) of a 7mm top saved the day.

Annual dives were around the 80,000 mark in 1994 but have now been restricted to 60,000 - 400 a day - to protect the reserve. Until recently few British divers were aware of what has been accomplished in these islands but they are catching on fast.

There are plenty of people who want a holiday for the family with some diving thrown in, but baulk at the thought of abandoning non-divers to the delights of Sharm or Hurghada for hours on end. Estartit makes an ideal compromise, with a reasonable beach, plenty of bars, restaurants, shops and a wide variety of accommodation, although it is a bit hectic at the height of the holiday season.

Charter flights go to Gerona only 30 miles away, where cheap car hire is available. However, many people choose to take their own vehicle, and with the European motorway system now running unbroken from Calais to within 20 miles of Estartit, the journey from the Channel can be accomplished in 10 to 12 hours.

Until I revisited Estartit, my enthusiasm for Mediterranean diving was in terminal decline. Clear water is great, but when there is little else to look at except my buddy, I wish I was back in the UK's murky but fruitful seas. While the marine life of the Medas Islands may not be quite back to what Cousteau described in The Silent World, the Catalan Government has demonstrated to other countries with impoverished marine environments just what can be achieved for their local economies with some determined action and good management.
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Unisub charges £130 for a ten-dive package, or £230 for one week's hotel and full board plus ten dives. Flights cost from £110 return. Contact the centre on 00 34 72 751768/fax 750539.