There is nothing quite like the moment a long, sweaty climb ends and a dark sheet of water appears between two shoulders of rock. Northern Britain is scattered with these small upland lakes — tarns in Cumbria, llynnau in Wales, lochans in Scotland — and most are reached only on foot. That is what makes a dip in one so memorable: you have earned it.
The water, though, is almost always colder than walkers expect. Even in late August, a tarn sitting at 600 metres may hover around 10 to 13°C, and in early summer, fresh from snowmelt, it can be nearer 6 or 8°C. That is a different proposition from a summer dip in a lowland river, so it pays to carry two simple pieces of kit: a tow float for visibility and a roll-top dry bag for the things you cannot afford to soak.
A tow float is an inflated bladder — usually bright orange, yellow or pink — worn on a waist belt and trailed behind you on a short leash. Its main job is to make you visible.
Choose a dual-chamber model if you can — two inflated bladders mean a puncture still leaves you with something floating. Inflate it at the water's edge rather than at the car, where warm air expands and makes a taut float awkward to handle in a breeze. Tuck the leash so it cannot snag on submerged rock or tree roots.
Be clear about what a tow float is not. It is not a life jacket or a buoyancy aid, and it will not keep an unconscious swimmer afloat. It is a marker, a rest stop and a kit carrier — valuable, but no substitute for judgement.
A roll-top dry bag is the second piece of kit worth its weight. The principle is simple: roll the top over three or four times, then clip buckle to buckle. Fold it flat rather than stuffing it full — a bulging bag will not close cleanly, and a crease in the roll is where water finds a way in.
Two bags work better than one. A large bag (15–25 litres) takes your dry clothes, towel, warm layer and boots; a small bag (2–5 litres) takes keys, phone, wallet and any medication. Keeping valuables separate means you are not unpacking everything to find a car key. If the bag has a lanyard or D-ring, clip it to your tow float belt or wedge it under a rock well above the waterline — a dry bag will happily float away on a gust of wind.
The walk in is often longer and rougher than the swim, so pack for the descent as much as for the water.
Upland water is cold enough to trigger a gasp reflex, so wade in slowly and let your breathing settle before you commit. Keep the first dip short — a few minutes is plenty on a first visit. Swim with someone if you can, and if you are alone, tell a reliable person exactly which tarn you are heading for and when you expect to be back. Phone signal on the fells is patchy at best.
Check the forecast for wind and cloud, not just rain. A tarn can be calm one minute and choppy the next, and a strong breeze makes the walk out far harder than the walk in. In cold months, keep the dip brief, dress fast and get moving downhill to warm up.
Upland tarns are fragile places. Keep to established paths to reach the water, avoid trampling bog vegetation, take every scrap of litter home, and never light a fire or use soap or shampoo. Park considerately at the road end and leave gates as you find them. In Scotland, access legislation is generous, but responsibility still comes first; elsewhere, be guided by local signs and common sense.
Do that, and the reward is the same each time: a cold, clean plunge, a bright float marking your place on the water, and the quiet certainty that everything you need is folded safely inside a roll-top bag on the shore.
Northern Tarn shares practical, down-to-earth guidance on upland tarns, fell walking and wild swimming in northern britain for readers across the UK.
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