Lake
Still water with a summer thermocline. The warm surface layer is thin — cross it and the temperature falls sharply.
| Spot | Type | Region | Max depth | Walk | January | August |
|---|---|---|---|---|---|---|
| Lake Bled, Velika Zaka A warm, small, spring-fed lake with a 6 km shore path and a designated bathing lawn on the south-west shore away from the island crowds. |
Lake | Gorenjska, Slovenia | 29.5 m | 3 min | 4.5° | 23° |
| Fuxian Lake, Luchong shore A deep rift lake on the Yunnan plateau with 155 m of depth and visibility over 8 m — biologically closer to Baikal than to a lowland Chinese lake. |
Lake | Yunnan, China | 155 m | 4 min | 10° | 23.5° |
| Qiandao Lake, Laoshan Bay An artificial lake with 1,078 islands, holding drinking-water grade Ⅰ water — so clean that the visibility below the surface reaches 7 m in winter. |
Lake | Zhejiang, China | 100 m | 5 min | 7° | 27° |
| Llyn Idwal A glacial cwm lake at 380 m in a rock bowl under Y Garn — a 25-minute walk in, no roads, no boats, and water so clear you can see the boulders at 6 m. |
Lake | Snowdonia (Eryri), Wales | 12 m | 25 min | 2° | 14.5° |
| Lac d'Annecy, Plage de la Brune The cleanest large lake in France, fed by Alpine snowmelt and filtered through a limestone aquifer — clear enough that the 30 m depth line is visible from a paddleboard. |
Lake | Haute-Savoie, France | 65 m | 2 min | 5° | 21° |
| Buttermere The Lake District's most swimmable lake: no motorboats, no development, a 7 km shoreline path, and a shingle spit that gives deep water ten metres from the bank. |
Lake | Lake District, England | 23 m | 6 min | 3° | 17° |
| Loch Morlich A shallow, sandy-bottomed loch at 300 m altitude with a pine-fringed beach — the only place in Britain where you can swim in a Cairngorm loch with a beach that would pass for a coastal one. |
Lake | Cairngorms, Scotland | 12 m | 3 min | 2.5° | 15.5° |
| Walchensee, Urfeld shore The deepest large lake in the German Alps — 190 m — and the reason it stays turquoise: a huge depth of water absorbs red light and reflects blue back. |
Lake | Bavaria, Germany | 190 m | 4 min | 4° | 19.5° |
Before you get in
Cold water is the one hazard that applies everywhere in this library. Below 15 °C the gasp reflex can make you inhale water involuntarily within seconds of immersion; below 10 °C, unacclimatised swimmers lose the ability to swim effectively within minutes. Enter gradually, keep your first session under five minutes, never swim alone, and get out while you still feel fine — the afterdrop continues after you leave the water.