South Wales and Mendip, Great Britain · about 7 km from Glynneath
Porth yr Ogof
Temporary, until 31 Mar 2027
Until March 2027 parking at Cwm Porth (the Porth yr Ogof car park) is very limited: the nearby Gwaun Hepste car park is closed. Caving groups can pre-book spaces at Cwm Porth with the National Park Authority.
- Max depth7 m
- CertificationIntro to cave
- Water temperature≈ 4–10 °Cestimated, no reports yet
- SpecialSidemount
Diving and fills
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Fills nearby
- Fill stationThe Lake (Cromhall Quarry)Air (232 and 300 bar), nitrox (22–100 %), oxygen and 'mixed gas'; which mixes exactly is not stated — askRoute ↗
What it looks like
Porth yr Ogof Cave diving beyond sump 1 Porth yr ogof cavern dive March 2014 Porth yr Ogof & diving in Dinas Silica Miane 🇬🇧 Upper Cave, Porth Yr Ogof
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Videos and posts
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Porth yr Ogof Cave diving beyond sump 1 Porth yr ogof cavern dive March 2014 Porth yr Ogof & diving in Dinas Silica Miane 🇬🇧 Upper Cave, Porth Yr Ogof
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Other people's footage, not advice: how someone else dives here says nothing about what suits your team. Dive within your training.
The dive
The water is usually clear, but the flow can be very strong. According to InDEPTH this is one of the few British sumps suitable for a two-diver team.
1 earlier accident or incident has been reported at this cave. Read what happened ↓
Profile and sections
The water is usually clear, but the flow can be very strong. According to InDEPTH this is one of the few British sumps suitable for a two-diver team. Water temperature is not published; British caves average 7–10 °C.
In this 2.25 km cave the Afon Mellte goes underground, and it resurges at the Resurgence Pool. The cave is heavily used by dry cavers (over 30,000 visitors a year) and as a training cave.
Practical: according to UKMC a cavern card is enough for the main section, while the upstream sumps need full cave. Most Welsh cave divers explore solo, the upstream section included (Caving Wales).
- Depth and profile
- Main section max ~-4 m, upstream ~-6 m; downstream ~250 m to the resurgence (UKMC). InDEPTH: max 250 m penetration, air bells at 150 and 200 m. Resurgence Pool -7 m. More sumps further into the cave (e.g. sump 9).
- Configuration
- Sidemount with small cylinders, helmet and hand-held light is the British norm; backmount is possible, but you carry everything through the cave. CCR makes little sense: short and shallow.
- DPV: Not DPV-suitable (estimate)
- Short, shallow sumps with flow and a carry through the cave: no gain.
Who can dive where
- At least Intro to cave
- Configurations: Backmount / twinset / Sidemount / CCR / Small cylinders / no-mount (speleo sumps)
- Goes down to 7 m (trimix or deco may be needed)
This is how the planner decides who in your team may dive this cave. Rules your own trip adds (organizer, a mail, the AI) show with your trip.
How to get there
No permit and no CDG membership needed: no access restrictions are known. The national park authority manages the entrances and the pay-and-display car park 50 m from the main entrance with visitor centre and warden, staffed every day except Christmas Day (summer 8:00–16:00, winter 9:00–16:00). Parking costs £6 per car and £7 per minibus, from 1 January 2027 £7.50 and £10; no camper vans, trailers or coaches. Book your space in advance, as the car park often fills with walkers and caving groups: (01639) 722309 or cwmporth@beacons-npa.gov.uk. You reach the sumps through the cave: entrance A leads straight into sump 1, entrance B gives access to sump 2 (upstream) and sump 3 (downstream). From the Tradesman's Entrance you dive sumps 3, 2 and 1; via the Top Entrance you start in sump 1 and save ~150 m of diving.
Around Porth yr Ogof
Fills1 fill station · 80 km
The Lake (Cromhall Quarry)
Cromhall Quarry, Wotton Road, South Gloucestershire GL12 8AA
Air (232 and 300 bar), nitrox (22–100 %), oxygen and 'mixed gas'; which mixes exactly is not stated — ask
Workshop Wed, Thu, Sat and Sun 8:00–15:00
Dive lake in a former quarry (max -17 m) with a technical department (IDEST-certified) for fills, servicing and cylinder testing; the workshop is by the quarry entrance. Diving at weekends, no solo diving. Not a dive school. No phone number or e-mail address on the website: contact through the form.
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Caves nearby2 within 29 km
News
All (1)
Accidents and incidents
What happened at this cave before, with the sources. No names are given; read it as a lesson for your own planning.
- Fatal diving accident at Porth yr Ogof in 1971.
Access and rules change: check what applies locally right before your trip. Source: GDELT Project and the news feeds of diving magazines. Search for more news ↗ Searched automatically, last on 13 Nov 2026.
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