Setting out where the water runs clear

A limestone stream is rarely muddy and rarely dull. Because the water has filtered down through fissures in the rock, it arrives at the surface already clear and rich in dissolved calcium, so the light gets right to the bed and you can see every pebble, every swirl of sand, every caddis case stuck to the underside of a stone. Walk beside it in April and you have one of the best free shows in the British countryside.

Choose a stretch of public footpath that follows the water rather than cutting across fields. You want a path that stays within a few metres of the bank for at least half a mile, so you can stop, look, and start again without feeling you are trespassing or holding anyone up. Wellington boots are worth the bother even in a dry spring: the margins are poached, and the best flowers grow in the damp flush just beyond them.

Cuckooflower in the wet ground

The first thing to watch for is cuckooflower, also called lady's smock. It appears from late March into May in exactly the places you would expect: rushy hollows, the soft ground where a spring seeps out of the bank, the untrodden strip between the path and the water. Look for four pale lilac-pink petals on a stem of 20 to 40cm, and a faint cress-like smell if you crush a leaf between finger and thumb.

It matters beyond its prettiness. Cuckooflower is the main food plant of the orange-tip butterfly, and the eggs are a lesson in patience: tiny, pale, and laid singly on the flower stalks. If you find an orange-tip drifting along the hedge line, slow down and watch where she settles. Then leave the plant alone.

Wood anemone on the higher bank

Where the valley side steepens and old woodland hangs over the path, look for wood anemone. The flowers are white, sometimes washed with pink beneath, and they behave in a very particular way: they open in sun and close in rain or at dusk, so a dull afternoon can make the whole bank look bare. Come back on a bright morning.

• Count the petals: usually six, held above a whorl of deeply divided leaves.
• Look at the pattern, not the plant. Large drifts mean old woodland, because anemones spread by rhizome at roughly a metre every few decades.
• Note the soil. Anemones prefer the slightly acid leaf litter on top of the limestone, not the lime-rich ground itself.

The habit of the short stop

Most of what you will miss, you will miss because you are moving. A gentle walk with five or six deliberate pauses will show you more than a fast one with none. The rule is simple: walk a hundred metres, then stop for three minutes. Stand still. Do not get the flask out yet, because rattling and pouring hides the sounds you came for.

Three minutes is long enough for the stream to stop being background noise and start being a set of separate sounds: water over a riffle, water under an undercut bank, the tick of a stone turning in the current. It is also long enough for a dipper to forget you are there.

Dippers, wagtails and the life of the stream

The dipper is the bird that justifies the whole walk. Dark brown, white-bibbed, short-tailed, it bobs on a mid-stream stone and then walks straight into the current, hunting caddis larvae and mayfly nymphs on the bed. Watch for the pale eyelid blinking as it feeds.

Dippers nest early, sometimes from March, on ledges behind waterfalls, in weirs and under bridges, and they are protected by law while nesting. Keep your distance, do not linger at a nest site, and keep dogs out of the water entirely between March and July. The same stretch may hold grey wagtail, pied wagtail, a flashing kingfisher, and a heron standing so still you take it for a post.

• Splash marks on a boulder mean a dipper has been feeding there.
• White droppings on a mid-stream stone usually mean a regular perch.
• A dry-stone weir or small waterfall is the most likely nest site on a limestone stream.

Reading the shape of the valley

Limestone gives a stream its architecture. Notice where the banks are undercut and where gravel has built up on the inside of a bend. Notice the riffles, shallow and noisy, and the pools, deep and quiet, alternating every few strides. Sketch a simple cross-section in your journal: two lines for the banks, one for the water, a few arrows showing flow.

Higher up, you may find tufa, a soft crumbly deposit where calcium carbonate precipitates out around mosses. On the tops, clints and grykes split the pavement into blocks, and the stream itself may disappear into a swallow hole and reappear a field away. That is worth noting: it explains why the water is so clear and so cold.

Keeping a journal you will actually use

A nature journal works best when it is small, cheap and always in your pocket. An A6 waterproof notebook and a pencil will do more for your memory than a phone. Write in the field, not in the car afterwards, because detail evaporates within minutes.

• Date, place and grid reference, time started and finished.
• Weather, temperature, cloud cover, and how high the water is running.
• First sightings: first cuckooflower, first anemone, first dipper. These become a record you can compare year on year.
• Two or three drawings, done quickly. Draw the shape of a leaf, the angle of a branch, the curve of a meander. Accuracy beats artistry.
• One line about how the walk felt. It sounds soft, but it is the line you will enjoy reading in ten years.

Five lines is a good entry. Twenty is a bonus. The point is not the notebook; it is that writing something down makes you look properly at the thing you are writing about, and looking properly is the whole reason for walking slowly beside clear water in spring.