Read the water before you commit

Most rivers in the British hills are little more than ankle-deep trickles you can hop across without breaking stride. That is exactly why they catch hillwalkers out. A river that was a friendly stream on your ascent can be a roaring, waist-deep torrent two hours later after heavy rain on a catchment you never saw. In the Lake District, Snowdonia, the Pennines and especially the Scottish Highlands, spate conditions build fast and drop slowly.

Before you think about stepping in, stop and look upstream. Is the water brown and carrying debris? Can you see the riverbed? A rocky, cobbled bottom is usually visible through clear water at wading depth. If you cannot see the bottom at all, that tells you something about depth and speed. Then listen. A dull, continuous rumble often means boulders are being rolled along the bed beneath the surface, which is a sign of real power. Look at the banks too for the debris line — the tidemark of twigs and silt left by the last high water shows how much the river has already come up.

Pick your line carefully

The shortest line across is rarely the safest. The obvious crossing point on the path is often narrow, deep and fast because it is where the water is funnelled between banks and boulders.

• Choose width over directness. A wide, shallow braided section with gravel bars is far easier than a narrow, deep channel, even if it adds distance.
• Avoid the outside of bends. That is where the current is fastest and the bank undercut. The inside of a bend is usually shallower.
• Never cross immediately above a hazard. Waterfalls, weirs, gorge sections, boulder chokes and fallen trees all become lethal if you slip and get swept into them. Plan your line so a fall sends you into a safe, shallow run-out.
• Think about the exit. A gentle gravel beach beats a steep, greasy mud bank you will struggle to climb out onto with wet boots.

Before you step in

Unclip your rucksack. Undo the waist belt and the sternum strap so the pack can be shed instantly if you end up swimming, but leave it on your shoulders — it keeps your core warm and can help you float. Extend your walking poles, and take your hands out of the wrist straps. A pole strap can trap your hand and twist your wrist or shoulder if you fall. Test the depth with a pole before you commit your weight to it, and be honest about what you find.

Keep your boots on. Bare feet and sandals have no grip on slimy rock and no protection from sharp stones, and numb feet make bad decisions. Wet boots dry; broken toes do not. Carry a dry bag with a spare fleece and socks for afterwards, and tell the rest of your group exactly where you intend to cross and who is watching from where.

Footwork, poles and posture

Turn side-on to the current, facing slightly upstream, and shuffle across in small steps rather than lifting your feet. Keep your knees bent, your weight low and your centre of gravity over your feet. Plant each foot deliberately, feeling the bed before you transfer weight — a rolling cobble or a sudden drop-off is the usual cause of a fall.

Use your poles as extra legs. Plant them upstream of you so they brace against the current, and check the bottom with them first. In stronger flow, three points of contact should be on the bed at all times. Move one limb at a time, never crossing your feet, and keep your eyes on the water and your footholds rather than on the far bank.

Crossing with others

Send the strongest and most experienced member of the group across first to confirm the line, then have them watch from downstream, ready to help. Where possible, only one person should be in the water at a time. Linking arms in a chain looks reassuring in photographs but works poorly in the small, fast rivers of the UK, where it makes everyone less stable rather than more. Agree a clear shout — a single word for "stop" — and respect it. Anyone who does not want to cross should be able to say so without argument.

If it goes wrong, and when to walk away

Cold water shock hits within seconds. The gasp reflex and sudden hyperventilation are involuntary, and even a summer river in the Highlands may sit at only 8°C. If you go in, try to control your breathing, float on your back with your feet downstream to fend off rocks, and look for an exit rather than fighting the current. Once out, get out of the wind, strip wet layers, get into dry kit, and keep moving. Watch for the signs of hypothermia: slurred speech, clumsiness, shivering that stops.

Finally, remember that the river will still be there next week. If the crossing looks marginal, turn back, take a longer route, or abandon the day and come back with lower water. The hills reward patience far more than they reward stubbornness, and no summit is worth a soaking in a spate. There will always be another day.