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Why the first minute is the one that matters

British rivers are cold all year round. A chalk stream in high summer might reach 14°C on a good day, and by January many rivers sit between 3°C and 6°C. Anything below about 15°C triggers cold water shock, and that reaction is not a matter of being tough enough. It is an involuntary reflex, and it happens to everyone.

The moment you enter cold water, you gasp. Your breathing rate can quadruple for the first thirty to sixty seconds, your heart rate and blood pressure spike, and your skin tightens with a sharp, panicky feeling. If your head goes under during that gasp, you can inhale water without meaning to. That first minute is where most cold water incidents begin. After the initial shock passes, the cold starts to take power from your arms and legs, so swimming that felt easy in a pool becomes hard work surprisingly quickly.

Understanding this changes how you swim. You stop treating the first minute as something to fight through and start treating it as something to manage.

Entering gradually, not bravely

Diving or jumping in is a shortcut to the worst part of cold water shock. Wading in slowly gives your body time to adjust and keeps your breathing under some control.

• Wade to your knees first, then your waist, and pause there.
• Splash cold water onto your face, wrists and the back of your neck. It sounds odd, but it helps your system accept what is coming.
• Lower yourself in rather than stepping off a bank into deep water.
• Keep your head above the surface for the first minute or two. A cold head adds to the shock.
• Do not swim off straight away. Float, hold your tow float, and let the gasp settle.

Stay close to the bank while you acclimatise. If your breathing does not come back under control within a minute or so, that is information, not weakness. Get out, warm up, and try again another day when you are better prepared.

Breathing is the skill worth practising

The single most useful thing you can do in cold water is control your exhale. Short, snatched breaths through the mouth keep the panic going. A long, slow breath out does the opposite.

Try breathing out through pursed lips as if you were gently blowing out a candle, and make the out-breath longer than the in-breath. Some swimmers hum, some count the seconds. Whatever works, give it your full attention for the first minute. If you are with others, chatting about something ordinary — the weather, what you are having for lunch — is remarkably effective at steadying everyone's breathing.

Once your breathing is calm and your hands are still working properly, you can start swimming. Repeat this settling routine every time you get in, even in summer. Familiarity does not remove the reflex.

Kit that buys you time and visibility

A brightly coloured tow float is the most valuable piece of kit a river swimmer can own. It makes you visible to boaters, anglers and anyone on the bank, and it gives you something to hold if you need to stop and rest. Tuck a whistle and a dry bag inside it.

• Wetsuit or swimrun suit in spring, autumn and winter, plus neoprene socks and gloves on really cold days.
• Grippy footwear for the bank and the riverbed. Riverbeds are slippery, and broken glass and sharp stones are common.
• Dry clothes, a hat and a warm flask left at your exit point, not back at the car.
• A head torch if there is any chance you will be finishing near dusk.

Leave the glass bottle and the heavy rucksack at home. Everything you carry should be able to float or be clipped to your tow float.

Swim with others and read the river before you get in

Never swim a river alone. Rivers change hour by hour, and rain falling ten miles upstream can raise the level and speed where you are standing. Check river level readings and flood warnings the day before and again on the morning. If the water is high, brown or moving faster than you can comfortably walk, save it for another day.

Look for the hazards that catch people out: weirs, which create recirculating currents below them; strainers, such as fallen trees and branches, which let water through but trap swimmers; undercut banks; and anything that could trap a foot. Never stand up in fast-flowing water — float on your back, feet downstream, and steer towards the bank.

Cover any cuts before you swim, avoid swallowing river water, and wash your hands before eating. A hot drink afterwards is not just a comfort, it is good practice.

Getting out safely, and knowing when to stop

Choose your exit point before you enter, and look at it from the water. Ladders, shallow gravel shelves and gently sloping banks are far easier than a vertical wall or a muddy edge. Cold muscles lose coordination, so plan to leave before you feel you need to.

Ten minutes is plenty in winter. Get out if you are shivering hard, if your hands stop working, if your speech slurs, or if you feel oddly calm and disconnected — that last one is a warning sign, not a nice feeling.

Climb out slowly and deliberately. On steep or slippery banks, crawl on hands and knees to keep your centre of gravity low. Strip off wet kit immediately, pull on dry layers and a hat, and warm up gradually with a drink and a walk. Avoid alcohol and hot baths straight away, as they can worsen the afterdrop that comes as cold blood returns from your limbs to your core. Warm up slowly, and let the shivering do its job.