WE DROPPED DOWN through the darkening green water, using our drysuit feeds as brakes to slow our descent. Our view downwards started to become less even, and then quickly revealed kelp and rock. A last blast of air and we stopped, hovering on the edge of a wall.
Kicking our fins, we started to move down the wall, which revealed itself as a cacophony of colour - pinks, greens, oranges and reds - bounteous life clinging onto the steep rock face.
Masses of jewel anemones provided the bulk of the colour, while clumps of dead mens fingers accentuated this with their soft polyp-filled yellows. Red-eyed crabs peered out from their crevices, eyeing us suspiciously while their larger edible cousins flexed their arms to lock themselves into their hidey-holes.
Everything was in a state of motion. Even at 20m, the swell had a noticeable effect. The massive kelp fronds waved about above our heads while, on a smaller scale, anemones swayed, waving their tentacles first one way, then another, as the ever-changing surge took them.
In the 15m-plus visibility, we were in a fairyland. The rock wall was part of a system of deep gullies, some only a couple of metres wide but many metres deep. As we worked up them into shallower water, the life in them became progressively smaller, until we ended up in what was clearly a surge gully complete with rock mill.
Here there were patches of bare rock - and plenty of pebbles lining the seabed, showing that the grinding action of these on the lower rock walls kept any marine life from settling here.
Working up the shallow walls revealed an enormous quantity of sea squirts and sponges - creatures that actually thrive in these areas of strong surging water.
We finally surfaced after well over an hour, exhilarated but with our air depleted. Above us were the steep cliffs of Gallan Head and heading towards us was our boat - the Cuma. Getting back aboard was surprisingly easy because Murdo MacDonald, the skipper, knows his job well and handles the 65ft vessel as though she were a fraction that size.
The location of this dive must be one of the best-kept secrets in Britain. If such diving were available in a more accessible area, it would be teeming with divers. As it is, Murdo has it much to himself most of the time, because Gallan Head is on the very exposed west coast of the Isle of Lewis in the Outer Hebrides.
Fortunately it is often diveable, as it is usually sheltered from the prevailing winds, though the swell can be high because, but for the Flannan Islands and St Kilda, there is nothing but open Atlantic to the west.
The whole coast on the easterly-facing side of Gallan Head is cliff. Below the water, it seems to be made up of bedrock intersected by numerous gullies, some of which cut into the cliff, forming caves, both with a clear surface and without.

Explorer in the jungle
The life here is abundant, with all the species typical of wild, exposed sites present. There are even a few crayfish about - we found one clambering through the kelp one day, looking for all the world like an explorer fighting his way through a jungle!
Fish, however, were not so abundant. Why this should be is not clear, although it does make one wonder about over-fishing. Those that were present included some of the most beautiful found in Britain - colourful topknots, John Dorys, anglerfish and scorpionfish, plus their smaller relatives such as the leopard-spotted goby.
It would be possible to spend a whole week diving at Gallan Head, but west Lewis offers many other sites. Weather is the decider of diveable locations, however, and in the force 4-6 conditions prevailing, this meant that the Flannan Islands were not possible. So we looked at the smaller islands at the entrance to Loch Roag, where the Cuma is based.
These islands or islets are as exposed as Gallan Head, but offer some shelter and very different, but equally stunning, diving. Many have caves or tunnels in and through them.
One tunnel goes right through one of the smaller islands but is very shallow in the middle, so can be dived only if the swell has dropped sufficiently. This was a very memorable dive site for me, because we were visited by a basking shark that cruised a couple of metres above our heads as we swam towards the tunnel!
The tunnel has vividly coloured walls, with masses of bright orange sponge covering it in parts. Its floor is covered in boulders on which little survives, again due to the buffeting by the swell and high seas. Once through the tunnel, it opens out first into a gully, and then into what can only be described as a gorge or valley. In visibility of around 20m, the view was superb.
Around the corner from the cave are more and very different dives. Here there is a submerged wall, only 5-6m high but teeming with colour and life.
This gives way to a boulder slope, which in turn leads onto a sandy seabed at around 24m. If this sounds boring, I soon found that it was not - as a seabird flew past me at this depth, clearly having a look to see what I was!

Not a pot
This mini-wall was so luxuriant that we dived it twice, the second time working in towards the island, and again finding ourselves in surge gullies and cavelets.
Much of the area remains barely explored, so we decided to look at one or two sites onto which Murdo had never dropped divers before. On our last day, we tried a smaller craggy islet that was not even potted. We soon learned why!
We dropped into 20m of water (quite close in) and found ourselves on a pretty bedrock seabed. Working along, we found large boulders with topknots and lobsters. A little further and we hit a stunning wall, 24m at the bottom and stretching up to near the surface.
This wall was not sheer, but had sufficient ledges and fissures in it to attract many marine creatures, both encrusting and mobile. Crabs and squatties had taken up residence where possible - in one crevice I saw half of a vividly coloured squattie before realising that it was simply the shed outer shell of one further back in the crevice. Near the top, the immense sheets of anemones were breathtaking in their beauty.
This is a wall I would rate very highly - different but possibly even better than those of Bofascadale or Canna. Rediving it later, we had an even bigger surprise.
We missed the wall from the first dive by only a few metres and found ourselves in a deep ravine with equally spectacular walls on either side. As we followed it, we found that the encrusting life became smaller and the slight current began to pick up. It explained the lack of potting, as any pots would quickly get swept away in strong tides. The rock walls were coated in squirts, sponges and anemones, with deep, wide cracks coated in lush dead mens fingers.
The current never became too strong but it did make the dive hard work, and we turned back after a time to ensure that we didnt get swept around the corner of the island.
As we had entered the water we had seen some seals playing in the waves, and four or five visited us on the dive - although they were clearly not used to divers and were rather wary.
On the surface, there was a stronger current, and for the first time Murdo had to manoeuvre to pick us up, as the boat was being tugged by the flow as he moved away from the island.
As a total contrast, we tried one dive inside Loch Roag. Its creatures were very different. Firstly, we landed almost on top of a bright red gurnard wandering across the mud, feeling for food with its modified fins. It didnt like our presence, and swam off after a minute or two.
Another curious fish that we found was a clingfish, only a couple of centimetres long. This little creature moved whenever my flashgun went off, looking in another direction as if it was trying to spot the culprit.
I would say that the west coast of Lewis offers diving as good, if not better, than most available in British waters.
There are inevitably downsides, which are both cost and accessibility. To get to Loch Roag involves driving to Ullapool, to the north west of Inverness, taking the ferry to Stornoway and then crossing Lewis. Unless you are fortunate enough to live in northern Scotland, this trek involves many miles, B&B and ferry fare.
The Cuma is the only boat operating out of Loch Roag, and offers non-diving trips too. She is cosy and warm. Cathy, Murdos wife, performs miracles in the galley (you can put on weight on this boat!). In Murdo, Cuma has an excellent skipper with a dry sense of humour.
A long trek northwards it may be, but its one well worth making.

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    The Cuma from the water
    a father lasher, doing its best to mimic a cobble like the one behind it
    sun lighting the kelp forest reveals the vivid colours and extraordinarily dense life below it
    skipper Murdo MacDonald looks out from the bridge
    Sometimes the colours of the undersea creatures - this is a Devonshire cup coral - are incredibly vivid
    This topknot blends in with the colourful seabed and is revealed only by differential focus
    The shallowest parts of some of the surge gullies were rock mills, ground smooth and rounded by boulders and pebbles in winter storms