There are few better ways to cool off after a walk than a dip in a mountain llyn (lake), with Yr Wyddfa (Snowdon) rising above you. Wild swimming in Eryri (Snowdonia) has grown hugely in popularity, and with good reason. But the water here is cold all year, many lakes are on private land or used for drinking water, and conditions can change quickly. This guide covers where swimming is welcome, where it is not, and how to do it safely. For more spots, see our wild swimming guide.
Where to swim in Eryri
Llyn Padarn, Llanberis
Llyn Padarn is the easiest and best-known place to swim in Eryri. It is a designated bathing water, which means Natural Resources Wales tests the water through the summer bathing season (15 May to 30 September), and it was rated Excellent in the Welsh Government’s 2025 bathing water classifications. The National Park lists it as a popular lake for swimmers and water sports, and it is where competitors start the Brutal Triathlon.
The lakeshore is easy to reach from Llanberis village and Padarn Country Park, with views up the pass towards Yr Wyddfa. Some areas are shallower than others, but the lake is large and deep in places, so stay within your depth if you are new to open water. Llanberis is also handy for the Snowdon Mountain Railway if you want to make a day of it.
Llyn Gwynant, Nant Gwynant
Below the southern flanks of Yr Wyddfa, Llyn Gwynant is one of the most beautiful lakes in the National Park and is named by the National Park Authority as popular for swimming and water sports. It is not a designated bathing water, so there is no official water quality testing, and you should not expect lifeguards. Park only in proper car parks and laybys, as the road through the valley is narrow and busy in summer.
Llyn Dinas, near Beddgelert
A little further down the valley towards Beddgelert, Llyn Dinas is smaller and more sheltered, and is also used by swimmers. Like Llyn Gwynant it is not a designated bathing water, so use your own judgement on water conditions, respect any signs from the landowner and leave no trace.
Llyn Cwellyn: please do not swim
Llyn Cwellyn, beside the road between Beddgelert and Caernarfon, looks inviting but it is a drinking water reservoir supplying parts of Gwynedd and Anglesey. The National Park is clear that swimming is not permitted in drinking water reservoirs, and Dŵr Cymru Welsh Water prohibits unauthorised swimming in its reservoirs. Strong winds also funnel down off Yr Wyddfa onto the lake. Enjoy it from the shore, or from the Snowdon Ranger path, which starts beside it.
Lakes where swimming is not allowed
Some of the best-known lakes are off limits. Llyn Idwal lies in a National Nature Reserve, and the National Park asks people not to swim or use water sports equipment in the lakes there. Many other lakes and rivers are on private land, so you need the landowner’s permission. If in doubt, ask, or swim somewhere else.
Cold water safety
Eryri’s lakes are fed by mountain streams and stay cold even in a heatwave. The National Park warns that there is a risk of hypothermia and cold water shock even in the hottest weather. Cold water shock makes you gasp and breathe fast, and it is the moment most likely to get you into trouble. Our Yr Wyddfa safety report includes recent incidents in mountain pools.
If you get into difficulty, the RNLI’s advice is to Float to Live:
- Tilt your head back, with your ears submerged.
- Relax and try to breathe normally.
- Move your hands and feet to help you stay afloat.
- It is fine if your legs sink, we all float differently.
Some other sensible habits:
- Never swim alone, and get in slowly rather than jumping or diving. Clear water can look shallow when it is not, and there may be hidden rocks.
- Wear a bright swim cap and take a tow float so you can be seen. A wetsuit helps with the cold.
- Stay close to the shore and know how you will get out before you get in.
- Cover cuts with waterproof plasters, wear footwear and try not to swallow the water.
- Have warm clothes and a hot drink ready for afterwards.
- In an emergency on a lake or in the mountains, call 999 and ask for the Police, then Mountain Rescue. At the coast, call 999 and ask for the Coastguard.
Water quality and blue-green algae
For designated bathing waters such as Llyn Padarn and the North Wales beaches, Natural Resources Wales publishes water quality results and, during the bathing season, pollution risk forecasts on its bathing water explorer at environment.data.gov.uk. Check it before you go, particularly after heavy rain.
In warm, settled weather, blue-green algae can build up in lakes. Natural Resources Wales advises that you cannot tell whether algae is toxic just by looking at it, so assume it is. If you see scum, mats or discoloured water, stay out, keep dogs out too, and follow any warning signs. You can report blooms to the NRW incident hotline on 0300 065 3000. Look after the lakes in return: follow Check, Clean, Dry with any kit to stop invasive species spreading from one lake to the next. On land, volunteers are tackling another invader: see invasive rhododendron in Eryri.
Sea swimming on the North Wales coast
If the mountains are under cloud, the coast is within easy reach. Colwyn Bay has a long sandy beach, and both Colwyn Bay and Colwyn Bay Porth Eirias were rated Excellent in the 2025 bathing water classifications. Nearby Llandudno’s North Shore and West Shore were rated Good, and the Imperial has a handy round-up of wild swimming spots if you are staying in one of the Llandudno hotels.
The sea brings its own risks: check tide times, choose a lifeguarded beach where you can, and if you are caught in a rip current, do not swim against it. Stay calm, float and signal for help.
Plan your swim
Most of these spots are easy to reach by car or bus. Our parking and transport guide has the options, and the where to stay guide covers bases close to the lakes. Mwynhewch (enjoy), and swim safely.
FAQ
Is wild swimming allowed in Eryri?
Yes, in many places, including Llyn Padarn and Llyn Gwynant. It is not allowed in drinking water reservoirs such as Llyn Cwellyn, and the National Park asks people not to swim in the lakes of the Cwm Idwal nature reserve. Many lakes are on private land and need the landowner’s permission.
Is Llyn Padarn safe to swim in?
Llyn Padarn is a designated bathing water and was rated Excellent for water quality in 2025. That covers water quality only, not personal safety. The water is cold and deep in places, and you should not expect lifeguards.
Can you swim in Llyn Idwal?
No. Llyn Idwal is in a National Nature Reserve and the National Park asks people not to swim or take part in water sports there.
How do I know if a lake has blue-green algae?
You cannot tell by looking whether algae is toxic. Avoid water with scum, mats or discolouration, follow any warning signs, keep dogs out and report blooms to Natural Resources Wales on 0300 065 3000.
