Pembrokeshire's waters are full of puffins, seals, blue sharks and dolphins. Get in the water with marine conservationists who know where to find them.
Pembrokeshire's coastline is one of the UK's richest marine environments, and most people never see it. Below the surface, kelp forests sway over rocky reefs, grey seals glide past in the shallows and, in the right season, puffins dive alongside you as you float above clear water. A guided snorkelling trip here is as much a wildlife trip as it is a swim.
Celtic Deep is Pembrokeshire's specialist marine experience provider, run by AIDA-certified freedivers and marine conservationists who have spent years exploring and documenting these waters. Their guided snorkelling sessions go to the best sites along the coast, including the seagrass meadows of the Daugleddau estuary and the open sea off Skomer Island, home to over 6,000 breeding pairs of puffins. If you want to go deeper, their freediving courses are AIDA-accredited and suitable for complete beginners.
Celtic Deep also run some more unusual trips: blue shark encounters in open water, Lundy Island expeditions from Tenby, puffin and seabird trips, and multi-day marine adventures. Every trip is low-impact and mission-led, with part of the proceeds going directly into marine conservation and education. If you've never been under the water in Pembrokeshire, they're very good people to go with.
The practical bits worth knowing before your snorkelling session with Celtic Deep.
Guided snorkelling sessions run from half a day to a full day. Multi-day expeditions are also available if you want more time in the water.
Groups are kept small, which is safer and means everyone gets a proper look. Celtic Deep keep encounters with wildlife and the environment low-impact.
You need to be a confident swimmer. Freediving courses require good breath-hold comfort. Snorkelling sessions are accessible to most adults and older children.
Wetsuits, masks, snorkels and fins are all provided. Bring a towel, warm layers for after and a dry bag for personal items.
Trips run spring through autumn. Puffin trips peak May–July. Blue shark season is July–September. Freediving courses run year-round.
Most sessions suit confident swimmers aged 10 and over. Freediving courses are typically adult-only. Check with Celtic Deep when booking.
Celtic Deep operate along the Pembrokeshire coast, from the Daugleddau estuary out to the open Atlantic. Click a pin to book.
A local team who know Pembrokeshire's marine environment inside out.
No previous experience is needed for guided snorkelling sessions. Celtic Deep's guides will brief you fully on technique and safety before you enter the water. You do need to be a confident swimmer and comfortable in open water. If you can swim 50 metres unaided, you're ready.
Freediving is breath-hold diving: exploring underwater without scuba equipment. Celtic Deep are an AIDA (Association Internationale pour le Développement de l'Apnée) accredited centre, meaning their courses follow internationally recognised safety protocols. Courses start with complete beginners and progress at your pace, always with a qualified freediving instructor in the water with you.
Pembrokeshire's waters are really good for marine wildlife. Depending on the season and location, you might encounter grey seals, puffins diving for sand eels, spider crabs, cuttlefish, colourful nudibranchs, dolphins, and in summer, blue sharks in open water. Celtic Deep's marine conservationists know where and when to look, which makes a big difference to what you see.
Pembrokeshire's sea temperature ranges from around 8°C in winter to 17–18°C at peak summer. All sessions provide wetsuits (typically 5mm), so you'll be warm and comfortable even in spring or autumn. For winter freediving training, thicker suits and hoods are provided or recommended.
Celtic Deep run pelagic (open water) trips offshore to encounter blue sharks, one of the best marine wildlife experiences in the UK. Blue sharks are naturally inquisitive and generally non-aggressive. You'll be in the water with a qualified guide, wearing a wetsuit and snorkel gear. Trips run July to September when blues are most reliably present in Welsh waters. Numbers are strictly limited for safety and conservation reasons.
Skomer Island has one of the largest Atlantic puffin colonies in southern Britain, with over 6,000 breeding pairs. The puffin season runs from late April to mid-August, with May, June and July being the best months to see them both on land and diving in the water around you. Celtic Deep's puffin and seabird trips book up fast, so it's worth booking well ahead.
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