How to Find Safe Wild Swimming Spots Using Ordnance Survey Maps

If you’ve ever stood at the edge of a glassy lake in the Lake District or watched a river tumble through a Welsh valley and thought “I want to swim in that,” you’re not alone. Wild swimming in the UK has never been more popular, and for good reason. But finding the right spot — one that’s safe, accessible, and actually legal to swim in — takes a bit more than a quick Google search. This is where Ordnance Survey maps become your best friend.

OS maps are packed with information that most swimmers never think to use. Once you know what to look for, you’ll be able to assess a swimming spot from your kitchen table before you’ve even laced up your walking boots. This guide walks you through exactly how to do that, covering everything from reading water features to spotting potential hazards and understanding access rights.

Why Ordnance Survey Maps Are Essential for Wild Swimmers

Google Maps and satellite imagery are useful, but they tell you very little about what a body of water is actually like at ground level. Ordnance Survey maps — particularly the 1:25,000 Explorer series — give you a much richer picture. You can see contour lines that reveal how steeply a riverbank drops away, symbols that indicate whether land is open access or privately owned, and detailed markings for features like weirs, footbridges, and waterfalls that could make or break a swim.

The OS Explorer series (orange covers) at 1:25,000 scale is the one you want for wild swimming research. Each centimetre on the map represents 250 metres on the ground, which is detailed enough to identify individual river bends, small lochs, and woodland paths down to the water’s edge. The Landranger series (pink covers) at 1:50,000 is better for planning longer routes but lacks the detail you need for assessing a specific swimming spot.

You can use physical maps, or access the same detail digitally through the OS Maps app, which lets you overlay mapping layers and drop pins on potential spots. The app is well worth the annual subscription if you swim regularly throughout the year.

Understanding Water Features on OS Maps

Lakes, Lochs, and Reservoirs

On an OS map, standing water is shown in blue. Natural lakes and lochs are labelled clearly — you’ll see names like “Tarn,” “Mere,” “Loch,” or simply “Lake” depending on where you are in the country. A tarn is a small mountain lake, typically formed in a glacial cirque, and these are often superb swimming spots in the Lake District and parts of Scotland.

Reservoirs are also shown in blue but are usually more geometric in shape and will often be labelled explicitly as “Reservoir.” Swimming in reservoirs is a more complicated matter (more on that shortly), so it’s worth identifying these before you get excited about a blue blob on the map.

Look at the shape of the shoreline. Natural lakes tend to have irregular, winding edges, while reservoirs often have straighter sections where they’ve been dammed. If you see a dam symbol — shown as a thick line across a watercourse — that’s a clear indicator you’re looking at a reservoir.

Rivers and Streams

Rivers are shown as blue lines, with width indicating relative size. A double blue line means the river is wide enough to be shown to scale at 1:25,000; a single line indicates a narrower watercourse. For swimming purposes, you want to be looking at where rivers widen, slow down, and deepen — features you can infer from the map even before you visit.

Contour lines are your friend here. Where contour lines are tightly packed near a river, the gradient is steep — the water will be fast-moving and potentially dangerous. Where contours are widely spaced and the river meanders in gentle curves, you’re looking at slower, calmer water that’s far more suitable for swimming.

River bends often create deep pools on the outer curve (where the current cuts into the bank) and shallow, gravelly sections on the inner curve. These natural pools — sometimes called plunge pools when they’re below small waterfalls — are among the best wild swimming spots in the country. You can often identify likely pool locations by spotting sharp river bends on the map, particularly in upland areas of Wales, Scotland, and the Peak District.

Waterfalls and Weirs

Waterfalls are marked with a specific symbol on OS maps — a series of short blue lines perpendicular to the watercourse, indicating a significant drop. While waterfalls create beautiful swimming pools at their base, they also come with real hazards: powerful hydraulic forces, submerged rocks, and unpredictable currents. Always treat waterfall pools with caution and never swim directly under a waterfall.

Weirs are man-made structures that create a controlled drop in a river. They’re marked on OS maps as a thick line across a watercourse, sometimes with the word “Weir” written next to it. Weirs are genuinely dangerous for swimmers. The recirculating hydraulic — where water pours over and then curls back on itself — can trap a swimmer and hold them underwater. Give weirs a very wide berth, both upstream and downstream.

Assessing Access Rights Before You Visit

This is where many swimmers come unstuck. Unlike in Scotland, where the Land Reform (Scotland) Act 2003 grants extensive rights of responsible access to most land and water, the situation in England and Wales is considerably more complicated.

England and Wales: Open Access Land

In England and Wales, the Countryside and Rights of Way Act 2000 (CRoW Act) established the right to access mapped open access land on foot. This land is shown on OS maps as a yellow tint with a specific open access symbol — a walking figure inside a circle. Open access land includes mountains, moors, heaths, and downs, but crucially, it does not automatically include the right to swim in water bodies on or adjacent to that land.

That said, in practice, many rivers and lakes in open access areas are swum in freely. The key is to get to the water via a legal route — a public footpath, bridleway, or open access land — and to be respectful of the environment. Look for footpaths (shown as dashed lines on OS maps) that lead directly to the waterside. These are your friend.

Public footpaths crossing a river via a footbridge, for example, may give you legal access to the riverbank at that point, even if the surrounding land isn’t open access. Many traditional swimming holes in Devon, Somerset, and the Brecon Beacons are reached in exactly this way.

Scotland: A More Generous Framework

In Scotland, the picture is much brighter for wild swimmers. The Land Reform (Scotland) Act 2003 gives everyone the right to be on most land and inland water for recreational purposes, provided they exercise that right responsibly under the Scottish Outdoor Access Code. This means you can legally swim in virtually any loch, river, or burn in Scotland, as long as you access it responsibly and follow the code — which covers things like leaving no trace, closing gates, and keeping dogs under control near livestock.

OS maps covering Scotland are just as useful for identifying the best spots, but you’re operating with much greater freedom than south of the border. Scotland’s Cairngorms, the Trossachs, Torridon, and the Isle of Skye all have extraordinary wild swimming available to anyone willing to do the legwork.

Checking for Restrictions

Even in Scotland, and even on open access land in England and Wales, some water bodies carry specific prohibitions. Reservoirs managed by water companies often ban swimming for water quality and safety reasons. Look for the reservoir symbol on the map and then check with the relevant water authority — United Utilities in the north west of England, Welsh Water (Dwr Cymru), South West Water, and so on — before swimming.

Some rivers pass through Sites of Special Scientific Interest (SSSIs), which are marked on OS maps with a specific notation. Swimming itself isn’t necessarily prohibited in SSSIs, but it’s worth being aware that these are sensitive environments and you should tread carefully.

Using Contour Lines to Judge Depth and Entry Points

One of the most overlooked skills for wild swimming research is reading contour lines in relation to water. Contours on a 1:25,000 OS map are spaced at 5-metre intervals (10 metres in more mountainous areas), and they tell you a great deal about what kind of entry and exit points you’ll find.

If contour lines run steeply right to the edge of a lake or river, you may be looking at a rocky, difficult entry with deep water immediately at the shore — which could be fine for confident swimmers but dangerous for beginners. Widely spaced contours approaching a waterside suggest a gentle, gradual slope, which usually means a shallower, more manageable entry and easier exit.

Look at multiple sides of a lake or tarn. A spot where a footpath meets a gently sloping shore with widely spaced contours is almost always going to be a better entry point than a steep, cliffed section of the same lake. Tarn Hows in the Lake District, for example, has sections of easy, shelving bank that are very obvious on an OS map and make it an accessible spot for swimmers of varying ability.

Identifying Hazards from the Map

Industrial and Agricultural Indicators

OS maps show a range of symbols that can flag potential water quality issues. Farms upstream are worth noting — agricultural run-off, particularly from livestock farms, can significantly affect water quality in rivers. Look for farm symbols (a cluster of buildings) upstream of your intended swimming spot. This doesn’t mean the water is definitely polluted, but it’s a factor worth considering alongside other water quality information.

Industrial buildings, sewage treatment works (marked on OS maps with the abbreviation “Sewage Works” or a specific symbol), and urban areas upstream of your spot are also relevant. The Environment Agency’s Bathing Water Quality data and the Surfers Against Sewage Safer Seas Service both offer real-time and historical water quality information for many UK swimming spots. Use these in conjunction with your OS map research.

Infrastructure and Navigation Hazards

Power lines crossing water are marked on OS maps with a specific symbol — a dotted line with pylons at intervals. Swimming near overhead power lines is not something you want to do, particularly in a storm. Railway lines running close to or alongside rivers and lakes are also worth noting — not because they affect water quality necessarily, but because they can mean limited access and potentially dangerous embankments.

Moving Forward

Once you have the fundamentals in place, the possibilities open up considerably. The UK offers fantastic opportunities for anyone interested in this hobby, and with the right foundation you will be well placed to make the most of them.