The Menai Strait, which separates the Isle of Anglesey from mainland North Wales, was described by Nelson as: one of the most treacherous stretches of sea in the world.
Whoever could navigate a ship here, could sail any sea in the world. Few would dispute his pronouncement; it is an area of overfalls, eddies and swirling water. It is not surprising, therefore, that the Swellies, as the Strait is affectionately known, has a wreck.
HMS Conway was a 96-gun line-of-battle wooden warship much like Nelsons flagship, Victory. Her ill-fated journey from her permanent berth off the stately home of Plas Newydd to Birkenhead for dry-docking and a refit in 1953 ended after only a couple of miles. She hit the Platters rocks, close to the shore just west of the suspension bridge, and a fire devoured what remained above the water. Nowadays she remains largely forgotten.
Oak, though, is solid stuff. Iron-hard baulks of it, along with a few copper rivets, washers and sheathing, is all that remains of the ship. These lie on the seabed, some partially covered, others standing proud, in just a few metres of water. As a wreck dive, the Conway is, perhaps, not up to much. But there are other good reasons for diving the Menai Strait. For it has recently been announced that the Secretary of State for Wales intends to designate the Menai Strait a Marine Nature Reserve - Britains fourth, and Wales second.
However, the area suffers from a credibility problem. Large quantities of suspended material are contained in the water, causing murkiness. This is not helped by summer plankton bloom and sediment that washes in after heavy rain. This means that little can be seen from above the surface to indicate that anything out of the ordinary lies beneath the water.
Under normal circumstances, visibility is far from good: 2-3m is quite common. Last years hot summer provoked exceptionally good conditions, though, with viz as good as 8m. One diver was heard to describe it as the best since 1964. Diving the Conway in such relatively clear water is like exploring a new site ... the surrounding topography actually becomes visible! It also means that the numerous inhabitants of the area can be seen as communities rather than iividuals. Most noticeable are abrupt changes in types of substrate and, along with these, equally distinct variations in the creatures living on them.
Descending from the shallows, an array of seaweeds and short kelp plants soon gives way to boulders and cobbles. These in turn drop quickly to larger boulders and bedrock; a few metres below these are shell gravel banks, and further on, small, cluttered mussel beds.
Sponges are prolific. Wherever there is a solid seabed - bedrock, boulder or oak - sponges dominate. Some lie in thin sheets, others seem to grope around with their long tendrils. Many are quite startling in their colouration: vivid reds, oranges, yellows and greens.
On any softer surfaces, anemones add their colour and delicacy to the robust sponges. Bushy hornwrack hydroids seem to give some spots the air of a country garden. Scrambling crabs and, less frequently, lobsters put an end to the illusion though.
Fish are not abundant. The most common here are butterfish, which swim off, snake-like, if disturbed. Long-spined sea scorpions sit unconcerned among the rocks. The few rock gobies on view flit rather more nervously. On the patch of mussels, colourful seaslugs search for anemones and hydroids on which to graze, while starfish pull open the mussels themselves.
To dive the Platters, it is possible to drift down from the bank below the suspension bridge before slack water, dive on the rocks during slack, and then drift back as the tide picks up in the other direction. A boat makes things a lot easier - the tide picks up quickly and becomes too strong to move against within a few minutes.
Diving in the Swellies at mid-tide is not a dive to be undertaken by the inexperienced. It is a rough roller-coaster ride giving fleeting glimpses of the changes in seabed. The current takes over and you have no control: stop, start, even backwards! And all of this as you constantly change depth. About all that is possible on this fast journey is to align yourself face forwards, concentrate on your buoyancy, hang on to your companion, and attempt to take everything in at the same time. Gravel, bedrock, cobbles, sand: it all whisks past. Patches of uncolonised rock attest to the strength of water flow.
You also provide convenient transport for some of the Straits residents.
Shore crabs release their grip on the seabed and frantically swim towards you. They grab hold of any suitable piece of gear - hoses are a favourite - and hitch a lift.
Football-sized lumps of green sponge slowly bounce along in the current. In 20 minutes it is quite possible to cover a mile or more, in water which can at times run at up to 8 knots. As the Strait is some 20 miles long, there are many sites to explore.
The dark hole near Pwll Fanogl, believed by some to be a massive pothole in the limestone, is nearly 30m deep. The murky water creates a much deeper feel.
The gradual slopes of small boulders and mud off Plas Newydd, and the nearby limestone outcrops, are home to creatures which can only be found on this type of rock.
Puffin Island, off Penmon, at the eastern end of the Strait, is a site for friendly seals and numerous dogfish.
While the Strait may not be everybodys idea of good diving, it has a fascination which appeals to many. Wreck divers might not be overly impressed, but for photographers and naturalists it provides species-rich, easily-accessible dive sites, which are sheltered enough to be available all year round.

Marine Nature Reserve  

Statutory Marine Nature Reserves (MNR) are set up with the aim of conserving features of biological and geological interest and providing opportunities for scientific study. They are administered by the national conservation agencies (Countryside Council for Wales, Scottish Natural Heritage, English Nature) with government funding. Unlike voluntary marine reserves, MNRs are legally protected.
In the case of the Menai Strait, its scientific and conservation value lies in its unique range of marine habitats and geology. Many species have had to make unusual adaptions in order to live in the narrow, rock-strewn central channel. There are also wide sand flats, rich in invertebrate life, which are important feeding and roosting sites for large flocks of birds. Geologically, it marks a fault zone dividing mainland north Wales from the older rocks of Anglesey.
There are no restrictions on diving in a MNR. Divers, however, are not permitted to damage or remove fish or the seabed. Shellfish may be taken.
Wales other MNR is at Skomer Island in the south west. Lundy Island and Strangford Lough are the other two in Britain. There are nine voluntary marine reserves in Britain.