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Rivers Are Wonderful, but They Are Not Swimming Pools

There is little to match the feeling of slipping into a clear, cool river on a warm afternoon — the tug of the current, the smell of water mint and wet stone, the sense of being properly immersed in the landscape. Wild swimming has grown enormously in popularity across the UK, and our rivers, from the chalk streams of Hampshire to the upland spate rivers of Wales and Scotland, offer some of the most beautiful places to do it.

But rivers are not static pools with a handy ladder. They change hour by hour with rainfall, they carry cold water even in August, and they hide hazards beneath a surface that can look deceptively calm. Almost every serious incident in river swimming comes down to the same handful of factors: flow, temperature, exits and hazards. Assess all four before you get in, and you will enjoy the water far more, not less.

Read the Flow Before You Read the Water

Flow is the single most important thing to judge. A river that was gentle last weekend can be a thundering, brown torrent after a night of rain in the catchment — and the rain may have fallen many miles upstream, out of sight.

• Check river level and flow gauges online before you travel. Many rivers have public monitoring stations showing levels, flow in cubic metres per second, and whether the water is rising or falling.
• Look for flood alerts and warnings for the area. If one is in force, choose another day or another stretch entirely.
• On arrival, look for tell-tale signs: debris lines on the banks, silt on grass, muddy water, trees and branches wedged in the banks at head height.
• Time the current with a floating stick over a measured 10 metres. Divide the seconds into 10 to get metres per second. Anything above roughly 1 metre per second is powerful; if you could not wade across it comfortably, do not swim in it.

Water is heavy stuff. At walking pace it can knock an adult off their feet, and at speed it will pin you against anything solid. If in doubt, stay out.

Cold Water Is the Quiet Hazard

Even in high summer, UK rivers often sit between 12°C and 18°C, and upland or spring-fed rivers can be colder still. In winter and early spring, 4°C to 8°C is common. Cold water shock — gasping, rapid breathing, a spike in heart rate and blood pressure — happens in the first minute, and it can overwhelm even strong swimmers.

• Enter slowly and deliberately, and let your breathing settle before you swim properly.
• Never jump or dive straight in, and never hyperventilate or hold your breath to "test" yourself.
• Consider a wetsuit in cooler months, and a brightly coloured swim hat and tow float for visibility.
• Keep sessions short in cold water and get dressed warmly afterwards — a hot drink and dry layers help.

Find Your Exit Before You Enter

The classic mistake is to walk upstream to a lovely deep pool and only then look for a way out. Currents push you downstream, so plan your exit downstream of your entry, not upstream of it.

Walk the bank first. Look for a shallow shelf, a gravel beach, a low grassy bank or a set of steps. Avoid steep, undercut or muddy banks that crumble when you grab them, and be wary of dense vegetation that hides the water's edge. If you cannot find a safe exit, you have found your answer: swim somewhere else.

Hazards Worth Knowing by Name

• Weirs and sluices: the recirculating "stopper" below a weir can hold even experienced swimmers under. Always portage well around them, on the bank.
• Strainers: fallen trees, branches and root balls let water through but trap people. They are among the most dangerous features on any river.
• Submerged debris: shopping trolleys, wire, glass, old fencing and rocks sit just below the surface, especially after spates.
• Foot entrapment: never try to stand up in fast, deep water — your foot can wedge between rocks in an instant.
• Water quality: avoid swimming for at least 24 to 48 hours after heavy rain, when agricultural run-off and storm overflows can enter the river. Blue-green algal blooms in late summer are another reason to stay on the bank.

Never Swim Alone in Unfamiliar Water

Swim with someone, or better still with a small group, in water you know. Tell a friend where you are going and when you expect to be back, carry a phone in a dry bag and note the nearest postcode or grid reference for the emergency services.

If you do get into trouble, float on your back, keep your airways clear and let the current carry you rather than fighting it. Go downstream feet first, steer towards the bank, and shout for help only when you have breath to spare. Rivers reward respect, preparation and patience — and they give back far more when you have taken the time to read them properly.