The dogfish lies motionless on the sandy ocean floor, a long, dark shape at ease with its environment. Two feet long, with dorsal fins that echo the shape of its bigger, deadlier cousins, the sharks, it remains immobile as four divers approach.

One of them slowly extends his hand, stroking it gently - a gesture repeated hesitantly by the others. Then, with a lazy wave of its tail, the dogfish moves forward and away, cruising past a clump of kelp and heading out of view.

We are a stone's throw from the Connemara shoreline, in Killary Harbour, but even at this depth there is much to see. Fifteen feet of water separate sand from air as fish, crabs and reefs combine to produce a spectacular landscape.

It is a vast palette of colour: eelgrass and sea lettuce grow in clusters on the seabed, their greens contrasting with the long brown leaves of kelp plants, which sway in the salty flow, and yellow clumps of plant-like anemone.

There is movement everywhere. Shoals of tiny wrasse shimmer, orange-brown pollock swim nervously away as we approach. Crabs move slowly along the sand, a soft platform that occasionally flickers into life as startled plaice dart from their camouflaged cover. Above us, jellyfish drift by, posing little threat to divers covered from head to toe in neoprene, but avoided nonetheless.

Communicating via a series of hand gestures, Cillian Gray, an instructor at Scubadive West, keeps tabs on the trio of beginners. Checking that we are OK, guiding us through exercises such as clearing water from face masks, he brings us gradually out to sea and points out the most notable flora and fauna.

Despite a brief childhood fear of water - as a six-year-old, swimming lessons saw me frozen on the poolside in terror - trying scuba-diving has long been an ambition.

Making this first dive in Connemara is even better than anticipated, the craggy stone hills that line Killary Harbour a striking backdrop for the exercise.

The day may be misty and the threat of rain never far away, but the landscape helps lighten spirits already giddied by expectation.

I couldn't wait to dive. But first, the three-hour session at Scubadive West began with a 20-minute safety briefing that explained the principle, equipment and procedure of diving. "Keep calm and breathe normally," advised Gray, a mantra he repeated as we stood in the shallows.

Trying to master the alien knack of breathing through a tube is hard, all the more so when struggling with the fins that make swimming easier but walking comical. A big part of the difficulty is the need to walk backwards (in order to avoid tripping over size-30 footwear), but compressed-air tanks and weight belts compound the awkwardness.

Get your balance wrong and you topple over with a splash; neoprene wetsuits insulate against the chill waters but do little to ward off embarrassment. I had the dexterity of a one-legged giraffe; it was a relief to move to deeper water.

For some, moving around on the seabed is initially a claustrophobic experience. The regulator in your mouth is the sole link with precious compressed air, and your instincts advise strongly against inhaling when immersed in several feet of very real, very wet seawater. But the fear subsides and the inhalation-expiration process becomes second nature once more, enabling you to get to grips with moving about.

The key is the breathing. At the beginning, I drifted upwards and away from the other swimmers or sank towards the sandy seabed. Some adjustments can be made by inflating or deflating the buoyancy control device, a life-jacket-shaped top linked to the compressed-air tank, but the diver's lungs permit the constant changes needed for true manoeuvrability. Inhale more air and you rise towards the surface, while less-expanded lungs enable you to scrabble along the seabed to stalk crabs and plaice.

Once you have mastered the technique, you have total freedom. Soar, dive, move slowly or speed along the depths, courtesy of those ungainly fins and some leg power. The control over buoyancy makes this the closest thing to flying and, combined with the amazing sights, means this is one of the most enjoyable things I have done. Roll on the next dive.