Scuba Diving and Snorkelling in Pembrokeshire

The water around the Pembrokeshire islands is protected, and it shows. The seabed off Skomer has been a marine reserve since 1990 and is now a Marine Conservation Zone, one of the longest-studied stretches of coastal sea in Britain, with kelp forest, jewel anemones, sponges and enough life on a single rock face to fill a dive.

Martin's Haven, on the tip of the Marloes peninsula, is the access point — the same slipway the Skomer boat leaves from. Dive charters run out to the islands from here and from the Milford Haven waterway, and the sites around Skomer, Skokholm and the Smalls are the ones people travel for. Everything out there is governed by the tide: Jack Sound between the mainland and Skomer runs at several knots, so dives happen at slack water and slack water does not last long. That is why local skippers are worth their fee.

Inshore, West Angle Bay is the standard shore dive and snorkel — sheltered, shallow, easy access, and full of the crabs, blennies and kelp that make a first snorkel worthwhile. Dale and Stackpole Quay both give easy entries into clear water, and Abereiddi's Blue Lagoon is a deep, still, sheltered quarry pool that dive schools have used for training for years.

The waterway also holds wrecks, and the coast off St Davids and the Smalls has been catching ships for as long as ships have come this way.

Visibility is the variable that decides whether a trip is memorable or muddy. The spring plankton bloom clouds the water into early summer; from June to September you can get 10 metres or more on the offshore sites, and rather less inshore after a blow. Wind, not rain, is what cancels a charter. Book with a few days' flexibility if you can.

Snorkelling is the underrated half of this. You need almost nothing, the shallows in the sheltered bays are full of life, and an hour with a mask at West Angle or in the kelp edges at Martin's Haven shows children more than any aquarium. A wetsuit makes it last twice as long, because floating still in 13°C water gets cold faster than swimming does.

What catches people out: how cold it is. This is dry-suit or good semi-dry territory in every month of the year, with a hood, and people who dive warm water abroad routinely underestimate a 12°C thermocline. Second, the tidal planning — sites here are not "turn up and jump in", and being swept off a pinnacle in poor visibility is the realistic accident. Third, the weather cancellation rate. A week of booked diving in Pembrokeshire is often four days of diving and three days of walking, and that is normal rather than bad luck.

The other thing worth knowing is that you will see seals. They will find you, come close, and mouth at your fins. It is the best part of diving here, and the right response is to float still, keep your distance in the autumn pupping season, and let them decide when they have finished with you.