Line & Net
The Art of Fishing

A fish is not swimming. It is standing still, and paying for it.

Say the word "fish" and almost everyone pictures the same thing: a silver shape travelling. Darting. Going somewhere.

Now go and look at a real one in a real stream. Find a clear shallow run on a bright day, stand well back from the bank, and let your eyes settle. What you will see is a fish that is going nowhere at all. It hangs. Its tail beats gently and the rest of it barely moves. The water is pouring past it — leaves, twigs, bubbles, all sliding away downstream — and the fish stays exactly where it is, as if someone had pinned it there.

That fish is not resting. It is working. Standing still in moving water costs something every single second, the way holding a suitcase out at arm's length costs something every second even though nothing is going anywhere. The fish is running, hard enough to stay in one place, and it has to keep doing it for the whole of its life, awake and asleep.

So a fish is not a traveller. A fish is a small animal holding position in a fluid heavy enough to resist every move it makes. Everything in this course grows out of that picture, so keep it: not a silver arrow going somewhere, but a creature braced against a river, all day, every day, for years. In a lake there is no current to brace against, but the heaviness does not go away — every metre it swims there, it has to shoulder aside.

The one fact that explains everything

Here is the sentence this whole course rests on. It is not about hooks or bait, and it sounds almost too plain to be worth saying:

Think of it as a ledger with two columns. On one side, everything the fish spends: holding station, breathing, growing, fleeing, chasing. On the other, everything it takes in: whatever food arrives and can be caught. The columns have to balance, and then some, or the fish gets thinner and then it dies. Not dramatically. Just quietly, over a few weeks, in a spot that looked perfectly good.

A wild fish has almost no slack in that ledger. It cannot decide to work a bit harder today and make it up tomorrow, because tomorrow is the same problem again. It has no fire, no shelter and no store cupboard worth the name. It has one lever, and the lever is this: be somewhere cheap, where food still comes.

So the question a fish is really asking, all day and all night, is not "where would I like to be?" It is:

Answer that question about a piece of water and you have found the fish. You have not guessed and you have not been lucky, and you did not need anybody to tell you about that particular river. You worked it out. That is the whole of this course, and everything after this is consequences.

The fluid that pushes back

To see why that ledger bites so hard, you have to feel what water actually is. Not wet — heavy.

Water is roughly eight hundred times as dense as air. That is why a stiff wind is a nuisance and a knee-deep current is a genuine problem. Stand in a river that is only up to your knees and moving at a brisk walking pace and you will find yourself bracing with your whole body. Now imagine being an animal small enough that the same river is over your head, with nowhere else to live.

There is a second thing about that push, and it is the important one. It does not grow gently as the water speeds up. Roughly double the speed of the water and the push against a fish goes up about fourfold. Treble the speed and it is up by something like nine times. The cost of standing still climbs far faster than the current does.

Run that back through the ledger and you get a result that surprises people the first time they meet it:

A hand's breadth. That is the scale we are working at. The difference between a spot that pays and a spot that bankrupts a fish can be the width of your palm — and it is invisible from the bank unless you know to look for it. Learning to see those hand's-breadth differences is, more than anything else, what people mean by reading water.

A cold engine

You are warm-blooded. You burn fuel constantly to hold yourself at one temperature, whatever the weather is doing outside. Nearly every fish you will ever meet does the opposite. It simply is the temperature of the water around it.

The proper word for that is ectotherm — an animal whose warmth comes from outside itself. There is no thermostat and no furnace. Put the fish in water at four degrees Celsius, which is about thirty-nine Fahrenheit, and the fish is at four degrees. Put it in water at twenty, which is sixty-eight Fahrenheit, and the fish is at twenty.

That matters enormously, because the speed of everything happening inside a body depends on its temperature. As a rough rule, good enough for our purposes: warm the water by ten degrees Celsius — eighteen Fahrenheit — and a fish's rate of burn roughly doubles. Cool it by the same, and the burn roughly halves.

So the ledger is not fixed. It is written in different sized numbers at different times of year, and both columns change at once.

• Cold water. The fish burns little, so it needs little. Its muscles are slow, so chasing anything is expensive and unlikely to work. It becomes extremely unwilling to spend.
• Warm water. The fish burns a great deal, so it must eat a great deal. Its muscles are quick, so a chase is cheap and likely to succeed. It becomes willing, even eager, to spend.

Hold on to that. In Part Four it turns into the single most practical piece of advice in this course — and it arrives as a conclusion rather than as a tip.

What a fish can sense — and what it senses of you

Before we go looking for fish, we should be honest about the fact that they are also looking for us. Not out of malice. Out of the same ledger: being eaten is the most expensive thing that can ever happen to you.

A fish has four ways of knowing you are there, and they are not equally strong.

Sight, through a circular window. This is the strange one, and it is worth getting right. Light bends when it crosses from air into water. The result is that a fish looking upward does not see the sky spread out across the whole surface. It sees the entire world above the water squeezed into one bright circle directly overhead — the cone of vision, often called the fish's window. That circle is a little more than twice as wide as the fish is deep. Everything outside it is not sky at all: seen from below, the underside of the surface behaves like a mirror, showing the fish a reflection of its own riverbed.

Inside the window, where something appears depends on how high it stands above the fish's horizon. Directly overhead — a heron on a branch, a bird passing — lands in the clear middle of the circle, bright and sharp. The lower down it is, the further out towards the rim it slides, and the nearer the rim it gets the more it is squashed, dimmed and smeared until the first ripple wipes it out altogether.

Here is the honest version of that, and it is more useful than the flattering one. A person on a bank is never anywhere near the middle of the window — you would have to be almost directly above the fish. You are always somewhere in the outer part of the circle. The whole question is how far out, and that is entirely under your control: standing up and close in lifts you well inside the rim, where you read as a solid shape. Kneeling and staying back drops you almost onto the fish's horizon, pinned against the very edge of the circle, where you are a smear that the smallest ripple erases. Same person, same fish, two completely different appearances.

The lateral line. Run a finger along the flank of any fish and you will feel a faint seam from gill to tail. That is a row of tiny pores, each holding a bundle of sensory hairs that bend when water moves against them. The lateral line is, in effect, a strip of skin that hears water. It picks up the pressure wave of a swimming fish, a dropped weight, and — this is the part that ruins people's afternoons — the thump of a boot on a soft bank, carried through the ground into the water.

Hearing. Sound travels through water about four and a half times faster than through air, and low sounds carry a long way in it. But there is a catch that decides which of your noises matter. Sound made in the air mostly bounces off the surface rather than crossing into the water — so talking on the bank is far less of a sin than people think. Sound made in or through the water does not bounce off anything. A boat hull knocked with a boot, a stone rolled underfoot, a tackle box dropped on aluminium, an anchor chain paid out — those are announcements.

Smell and taste. Far better than ours, and dissolved into a medium that carries scent downstream in a long plume. Some species hunt almost entirely by it in coloured water.

Which gives us the first piece of practical craft in this course — and notice that it was derived rather than handed over:

Therefore: the seam

Put the ledger and the pushing fluid together and something falls straight out.

The fish wants slow water, because slow water is cheap. But the fish also wants food, and in a river food is delivered — insects, larvae, small fish, anything that has lost its grip upstream comes tumbling down on the current. The fastest water carries the most food past a given spot in a given minute. So the fish wants fast water too.

Those two wants pull in opposite directions, and there is exactly one place that satisfies both at once: the line where fast water runs alongside slow water. That line is called a seam. The fish sits on the slow side of it, spending almost nothing, with its nose a few inches into the larder.

That is the most useful sentence in river fishing, and almost nobody is told it before they are handed a rod. Once you have it, a river stops being a stretch of water and becomes a set of lines — and you fish the lines.

Two words will keep coming up, so here they are. A tongue is the main thread of quick water running down a stretch — the tapering fast lane you can usually see as a smoother, darker or faster-moving band. A margin is the slower water along either side of it. A seam is simply the join between the two.

Seams announce themselves once you know the signs. Look for a line of bubbles or foam running downstream: foam collects along boundaries, so a foam line is a seam you can see from twenty paces. Look for a change of surface texture, choppy beside smooth. Look for a change of colour where deeper water meets shallow. Every one of those is the same thing wearing different clothes.

Therefore: structure is a machine for making slow water

If the fish wants a seam, then anything that manufactures one is worth its weight in gold. And a great many things manufacture one, all by the same trick: put an obstruction in moving water and the water must go around it, which leaves slow pockets behind.

The general word for such obstructions is structure — anything that interrupts open water. It is worth walking through them one at a time, not to memorise a list, but to notice that they are all the same idea.

• A boulder. Two good spots, not one. Behind it is the obvious one: a pocket of slack water, often with an eddy — water actually turning back upstream. But there is also a cushion of slow water pressed against the front of the rock, where the current piles up and stalls before splitting. Fish hold in both, and the front cushion is the one everybody walks past.
• A fallen log, or a root wad — the torn-out plate of roots at the end of a toppled tree. The same slack pockets, plus a roof overhead, plus a place for the fish's own food to live. Three benefits from one object.
• An undercut bank. Water has scooped a shelf out beneath the turf. It is dark, it is slow, it has a ceiling, and the current runs past the doorway carrying lunch. If a river had a best address, this would be it.
• A drop-off. Where the bed suddenly deepens. The deep side is slower and darker; the shallow side is where food is produced and warmed. The lip between them is a seam that happens to be lying flat.
• A weed bed. Weed slows water to a crawl inside itself and speeds it up around the outside, and it is crawling with small living things. The weed edge — the outer wall of the bed — is one long seam, and often the best feature in an entire lake.
• A bridge pier, a jetty, a sunken car, a shopping trolley. The river does not care what the obstruction is made of, and neither do the fish.
• The riverbed itself. This is the one people miss. Water rubs against the bed and slows down there, so there is always a thin, slower layer hugging the bottom — sometimes only a few inches deep. A fish lying on the gravel with its belly almost touching is sitting in the cheapest water in the river while the expensive water roars over its back. That is why so much of fishing happens near the bottom, and why an offering drifting a foot too high goes past unnoticed.

The old angling books split holding spots into three kinds, and the split still earns its keep. A holding lie is somewhere safe and cheap where a fish rests but eats little. A feeding lie is somewhere with food streaming past but little shelter, where a fish goes to eat and does not linger. A prime lie does both at once, and there are very few of them. Prime lies are occupied by the biggest fish in that stretch, and when that fish is removed, another moves in within days.

Therefore: every edge, of every kind

Now push the idea harder. A seam is one specific edge — fast water beside slow. But the reason a seam works is more general than current, and once you see the general version you can find fish in water that has no current at all.

An edge is any place where two conditions meet. It concentrates life for two separate reasons, and both of them are the ledger again. First, small creatures gather at boundaries, because boundaries trap and funnel things. Second — and this is the predator's reason — an edge lets an animal sit in one condition while hunting into the other. Hidden here, feeding there.

So look for edges of every kind:

• An edge of light. The shade line under a bridge, a stand of trees, an overhanging bush. A fish in shade looking out into bright water sees everything; anything in the bright water looking in sees nothing. Dawn and dusk work for the same reason and not merely by tradition: many hunting fish see better in dim light than the small fry they are hunting, so at first and last light the hunter's advantage is at its widest and open water it could not profitably use at noon becomes worth crossing. For most of the year those are the two best hours of the day — Part Four will show you the season that reverses it.
• An edge of temperature. A cold spring seeping in during a heatwave; a shallow bay warming first in spring; the outflow of a lake. Fish crowd a temperature edge the way people crowd a doorway.
• An edge of depth. Any drop-off, shelf, gravel bar or channel lip.
• An edge of cover. The wall of a weed bed, the outer branches of a sunken tree, the line where the lily pads stop.
• An edge of colour. After rain, a muddy stream running into clear water leaves a visible boundary — a mudline. Predators patrol the clear side of it and ambush into the murk.
• An edge of oxygen. Broken, tumbling water traps air and mixes it in. Below a small waterfall, a low dam or weir, or a stony riffle — the shallow, rippled, fast section between deeper stretches — the water carries more dissolved oxygen, meaning oxygen actually mixed into the water itself, which is the only oxygen a fish can breathe. In hot weather this becomes the most important edge in the river.

Notice that we have not left the one fact behind. Every edge on that list is a place where a fish can get more of what it needs for less than it would cost elsewhere. That is all an edge ever is.

Still water — where the seam goes when the river stops

A lake looks as though it breaks the rule. Nothing is flowing, so nothing is delivering, so surely the fish could be anywhere?

They could be. They are not. The rule has not gone away, it has only changed costume, and there are three things to look for.

First: the wind makes the current. Wind pushes surface water across a lake and piles it up against the downwind shore, where it sinks and returns along the bottom. That circulation carries floating food — and plankton, and everything that eats plankton — into the wind-battered bank. It feels wrong to walk into the wind, with waves slapping and casting made awkward. Do it anyway. On most lakes on most days the ugly bank that the wind is blowing into is the productive one, and the pretty sheltered bank is empty. Sailors would call that battered shore the lee shore, anglers usually call it the windward bank, and the words pull in opposite directions — so ignore both and just ask which bank the wind is driving the water at.

Second: the drop-off is the seam. With no current to sort water into cheap and expensive, the organising line becomes depth. Fish patrol the lip where shallow turns deep, because it lets them rest in the safe dark and feed up onto the productive shallows. Find the drop-off and you have found the road they travel.

Third: still water sorts itself into layers. In summer a lake often separates into a warm upper layer and a cold lower one, with a surprisingly narrow band between them where the temperature changes fast. That band is called the thermocline. It matters because in a rich, weedy or murky lake the cold bottom layer often runs short of oxygen by late summer — nothing is stirring it, and everything decaying down there is consuming what oxygen is left — so the fish are squeezed into the layer above. (In a clean, thin, rocky lake the deep water may stay perfectly breathable all summer, so this is a thing to check rather than a thing to assume.) A whole lake can concentrate its fish into a few feet of depth, and the person fishing at the wrong depth catches nothing all day and blames the fish.

Therefore: a fish faces into the current

Watch that fish in the stream again. It is pointing upstream. Nearly every fish in that river is pointing upstream. It is so consistent you can use it as a compass.

Two reasons, and both are the ledger. A fish is shaped to slip through water nose-first, so facing into the flow is far cheaper than being shoved about sideways — the same reason you turn to face into a gale rather than let it barge your shoulder. And a fish breathes by taking water in at the mouth and passing it out over the gills, which is the same direction the current is already travelling if the fish faces upstream — so part of the work of breathing is done for it, and done for nothing.

One correction before we build on it, because the rule is really about the local current rather than the river as a whole. A fish sitting in an eddy, where the water has turned back on itself, faces the way that pocket of water is going — which is downstream. So the rule is: a fish faces into the flow it is actually sitting in. In most of a river that means upstream, and in the slack behind a boulder it can mean the opposite, which is worth knowing before you wonder why your offering is arriving at the back of a fish's head.

But here is the consequence that changes how you fish, and it is bigger than it first looks. If the fish is facing upstream, then everything it has ever eaten came from upstream, drifting down towards its nose. That is what food looks like to a fish: something coming down the current at exactly the speed of the current, because it is being carried by the current and has no say in the matter.

Two immediate practical results, both derived rather than remembered:

• Work upstream where you can. Walk up the river and you approach fish from behind, in their blind spot, and any silt you kick up drifts away behind you. Walk downstream and you arrive in full view, pushing a warning wave and a cloud of mud ahead of you into every fish you were about to try for.
• Cast above the fish, not at it. The offering needs room to land, settle, sink and start behaving like debris before it reaches the fish's nose. Dropping it on the fish's head announces that something fell out of the sky, which is the one thing food never does.

The drift, and the one thing that ruins it

So the offering drifts down. Simple enough — until you remember that it is attached to a line, and the line is lying in the water too.

Here is the problem, and it is the great hidden problem of river fishing. The current is not one speed. The middle usually runs faster than the edges. If your offering is in slower water near the far side, and a length of line is lying across the fast middle, then the fast middle carries the middle of your line downstream quicker than the offering is travelling. The line bows into a downstream curve — a belly — and once that belly has any size to it, the line begins to pull. Your offering stops drifting and starts skating across the current, dragging a small wake behind it.

That is called drag, and it is the reason most drifts fail. Not the pattern, not the colour, not the knot. To a fish, an offering that skates sideways across the flow is not food behaving suspiciously — it is not food at all. It has never once been food. Nothing edible has ever moved like that.

The cure is called a mend: after the offering lands, you lift the middle of the line and lay it back upstream, so the current has to eat through that slack before it can start pulling. It buys you seconds of honest drift, and honest seconds are what you are actually fishing with.

The same reasoning now explains a retrieve. Wind a lure in fast and it crosses the fish's window in a moment, travelling in a direction and at a speed that no drifting food ever manages. The fish has to decide, in that moment, whether to leave its cheap water and spend hard-won energy on a sprint into the expensive water — for a target that is already leaving.

Which is not at all the same as saying fast never works. It works in a specific situation, and you can now predict the situation instead of memorising it: fast works when the chase is cheap and likely to succeed. Warm water, so the fish's muscles are quick and its appetite large. A predator built for ambush, sitting in cover, for whom a short violent burst is a normal day's work. And prey that genuinely does flee — a small fish bolting, which is the one natural thing that does move fast and across the flow.

Under those conditions a fast retrieve is not unnatural at all. It is an accurate imitation of something running away, and it triggers a chase because the sums work. Change any one of those conditions and the sums stop working, and the same lure at the same speed becomes invisible.

Therefore: cold water, slower fish, slower everything

Bring back the cold engine from Module 4, run it through the ledger, and out comes the most useful seasonal advice in fishing — not as a rule to trust, but as a conclusion you can check.

In cold water the fish burns little, so it needs little. Its muscles are sluggish, so any chase is slow, clumsy and unlikely to succeed. Both columns of the ledger have shrunk, and the spending column has shrunk hardest. Therefore the fish becomes almost unwilling to move at all.

Everything follows from that:

• Slow the offering down. Far more than feels reasonable. In genuinely cold water the offering should be barely doing anything — inching, hanging, drifting with the current and no more. A retrieve that is lively in June is invisible in February, because the fish has priced it and declined.
• Put it right on the fish's nose. A cold fish will not travel two feet to intercept something. It may not travel six inches. Your margin for error collapses, so depth and accuracy matter more now than they ever will again.
• Fish the deep slow water. In winter fish abandon the fast, thin, expensive runs and pile into deep pools and slack margins where the current costs them next to nothing. The riffle that was stuffed with fish in July can be genuinely empty in January.
• Expect a soft take. The take is the moment the fish draws your offering into its mouth, and it is the only moment you get. A cold fish does not seize anything. It moves a few inches, opens its mouth, and the offering is simply gone. If you are waiting for a bang you will miss the whole day.
• Fish the warm part of the day. In winter that is the middle of the afternoon, once the sun has put a degree or two into the shallows — the exact reverse of summer, where dawn and dusk win.

The other end — warm water and thin air

Run the same reasoning the other way and you would expect warm water to be simple good news: quick fish, big appetites, willing chases. For a while it is. Then it turns, and the reason is a second variable that only shows up at this end.

Warm water holds less dissolved oxygen than cold water. That is a plain physical fact about gases and liquids, and it produces a nasty squeeze: exactly when the fish's engine is running hottest and demanding the most oxygen, the water is able to supply the least.

So in a heatwave a fish is not lazy — it is short of breath. And it does the only thing it can. It goes looking for oxygen, which means the edges from Module 8 become the whole game:

• Below riffles, weirs and small falls, where tumbling water has beaten air into itself.
• At cold spring inflows and the mouths of cold feeder streams — sometimes a startling number of fish stacked into a few square metres.
• In deeper, cooler water — but only down as far as the layer where oxygen still reaches. Deeper is not automatically better in high summer.
• In and under weed by day, which is producing oxygen in the sunlight. Note that weed does the reverse at night, which is one reason a still, hot, weedy pond is at its very worst just before dawn.

The tackle, worked out from first principles

Tackle shops are overwhelming because everything in them is presented as a separate invention. It is not. Nearly every item is answering one of two questions: how do I make the offering behave like food? and how do I stay attached to a strong animal in a fluid that is pushing on everything?

• The hook. A bent spike whose point is set slightly off the line's pull, so that tension rotates it into a hold rather than sliding it out. The barb — the small backward spur near the point — exists to stop it reversing. Pinching that barb flat with pliers costs you a few fish and saves a great many, because it lets the hook come out of a fish, a bird, a dog or your own hand without tearing.
• The line. Long, thin and strong, and every one of those words is a compromise. Thinner line is harder to see, sinks better and drifts more honestly — and breaks sooner. The right line is the thinnest one that will hold the fish you might actually meet among the snags actually present — the sunken branches, roots and rocks that a hooked fish will run straight into.
• The leader and tippet. The leader is the clear, tapering length between your main line and the offering; the tippet is the final, finest section that the hook is tied to. The taper exists so that energy travels smoothly down the cast and the leader turns over — straightens out ahead of the line — so the offering lands first and lands gently. The fineness exists because those last two feet are the part lying right beside the fish's face.
• Weight. A split shot — a small soft pellet of metal, slit down one side and pinched onto the line — or a weighted hook is not there to help you cast further. It is there to get the offering down into the cheap slow layer near the bottom where the fish is actually living — and to get it there fast enough that it is deep before it reaches the fish rather than after.
• The float. Two jobs, and the second is the real one. It shows you a take — and it holds the offering at a chosen depth while the current carries it, giving you a controlled drift you can watch from thirty paces.
• The rod. A spring. It flings a light thing a long way by storing your effort and giving it back, and then, once you are attached, it cushions every lunge so that sudden loads never reach the thin end of your line. A rod is a shock absorber that happens to also be a catapult.
• The knot. This one follows straight from the second problem. Line is strong when it is pulled straight and weak where it is bent sharply and squeezed against itself, which is exactly what a knot is — so the knot, not the line, is where the connection is designed to fail, and it will. Therefore treat it as the weak point it is: wet it before you draw it up, so the coils slide into place and bed down evenly instead of binding and scuffing where they cross; pull it up slowly and firmly rather than snatching; and trim the tag end close. That single habit prevents more lost fish than any other change you can make.
• The net. Not a luxury. A knotless, soft mesh, held in the water so the fish never touches dry land or dry hands, is the difference between a fish that swims off and a fish that dies quietly an hour later.

Net, trap and weir — the same reasoning without a rod

A rod and line catches one fish that has decided to eat. Nets and traps do something cleverer and much older: they catch fish that have decided nothing at all, by exploiting the way fish already move.

The principle is the one we have been using all along, turned around. A fish is unwilling to spend. Therefore a fish meeting an obstruction will not usually smash through it or leap it — it will slide along it, looking for the cheap way past. So if you build a wall at an angle across a current and leave one gap in it, almost every fish that meets that wall will find the gap and go through it. You do not have to catch the fish. You only have to know which door it will choose.

That is what a weir is, in the older fishing sense of the word — a different thing from the low dam of the same name in Module 8: a fence of stones, stakes or brushwood set across flowing water, angled so that it funnels fish into a basket or a pen. Wooden fish weirs are among the oldest human structures found preserved in waterlogged ground, and they turn up across the world in forms so similar that people plainly worked the same idea out independently many times over. The same reasoning runs through a fyke net — a bag net held open by hoops, with funnel-shaped throats inside that are easy to swim into and awkward to find your way back out of — and through every lobster pot and eel trap ever built.

It runs through a hand net, through a cast net — a weighted circle of mesh thrown to fall over a shoal and close beneath it — and through a seine, a long wall of net hung between a floating top rope and a weighted bottom rope and drawn through the water or around a shoal until it closes. All of them are, at bottom, the same argument: put a barrier where the fish is already going, and let the fish's own thrift do the work.

Reading a stretch of water in ten minutes

Here is the test. You are standing beside a piece of water you have never seen, with nobody to ask and no report to read. What do you do?

You do not fish. Not for ten minutes. You sit down, low, back from the edge, and you ask the questions in order — and every one of them has already been answered in this course.

• Where is the current, and where is it not? Read the surface. Throw leaves if you cannot read it. Find the fast tongues and the slack margins, and draw the lines between them in your head.
• Where are the seams? Foam lines, colour changes, the boundary where choppy meets smooth. Mark the best two or three.
• What structure is making slow water? Boulders, logs, undercut banks, weed edges, bridge piers, drop-offs. Remember the cushion in front of a rock, not only the pocket behind it.
• Where are the other edges? Shade lines, depth changes, weed walls, an inflow, a mudline, broken oxygenated water.
• What is the temperature, and what does it buy me? Cold: deep, slow, close, patient. Warm: shallow, quick, oxygen, early and late.
• Which way will the fish be facing, and how do I get behind them? Plan the approach before the first cast, not after you have spooked the pool.
• Where does the sun put my shadow? Move so that it falls on the bank behind you and not on the water in front of you.
• How does my offering get there behaving like food? Which side do I cast from, how far above, and where will the line be lying once it lands?

Answer those eight and you have a plan built entirely out of things you can see, none of which required local knowledge. That is what understanding buys you over a list of tips: a list only works on the water it was written for.

The fish in your hands

Everything up to here has been about persuading a wild animal to make a mistake. What happens in the ninety seconds afterwards decides whether that animal is still alive next week, and it is the part of the craft that separates people who enjoy fishing from people who can be trusted with a river.

If you are keeping the fish to eat, kill it immediately and properly with a single firm blow to the head — do not let it suffocate slowly in a bag. That is both the decent thing and the thing that makes it taste better. If you are putting it back, the whole business comes down to minimising two things: time out of water, and damage to the skin.

• Play it hard and land it quickly. A long, gentlemanly fight is the single biggest cause of fish dying after release. Use tackle strong enough to end things.
• Wet your hands first. A fish is coated in a slime layer, which is its skin's defence against infection and parasites. Dry hands, dry grass, a dry rock or a dry towel strip it off, and what swims away has been given an open wound it cannot see.
• Keep it in the water. Unhook it in the net, in the shallows. Every second in air is a second it cannot breathe, and a fish held up for photographs is a fish being suffocated for a photograph. If you must lift it, hold your own breath while you do — when you need air, so does it.
• Support it properly. One hand under the belly, one lightly at the tail. Never hold a fish by the gills, and never hang a heavy fish vertically by the jaw — its organs are not built to be carried by its own jaw hinge.
• Hold it facing the current until it goes. Do not push it back and forth; that forces water the wrong way through the gills. Just hold it upright, nose into the flow, and wait. It will tell you when it is ready by leaving.
• If it is hooked deep, cut the line. Digging for a hook in the throat kills far more fish than a hook left in place, which will often work loose or corrode away.

Therefore, therefore, therefore

If you followed all of that, you were not handed a list of tips. You were handed one fact and its consequences — and it is worth seeing the whole chain laid out end to end, because the chain is the thing you are keeping.

A fish is a machine for spending as little energy as possible. Outside of breeding, it must take in more than it burns, and it lives in a fluid heavy enough to charge it for every movement — and, in a river, to push on it whether it moves or not.

Therefore it holds wherever food arrives for the least effort spent holding station. Therefore, since the push rises with the square of the speed of the water, so that halving the speed quarters the push, a hand's breadth sideways out of the quick water is worth a fortune to it. Therefore the one place that satisfies both wants at once is the line where fast water runs beside slow — the seam — and the fish sits in the slow side and eats what the fast side delivers. Therefore structure matters, because a rock, a log, an undercut bank, a drop-off and a weed edge are all machines for manufacturing a slow pocket next to a fast one. Therefore the fish faces into the flow it is sitting in, that being cheapest and its breathing coming half-free with it, and therefore everything it has ever eaten came down to it from upstream, drifting at the speed of the water. Therefore your offering must arrive from upstream, drifting at the speed of the water — and therefore drag, where the line bellies in the fast lane and hauls your offering across the flow, is the great destroyer of good drifts. Therefore an unnaturally fast retrieve is not frightening but simply too expensive to chase, and therefore it only works when the chase is cheap: warm water, quick muscles, and prey that genuinely does flee. Therefore cold water, which roughly halves the fish's rate of burn, means a slower fish, a smaller appetite, a shorter reach and a presentation slowed far past what feels sensible. Therefore warm water means the opposite, right up until the oxygen runs short, and then it means edges again. Therefore edges of every kind — current, light, temperature, depth, weed, colour, oxygen — concentrate fish, because an edge is always somewhere an animal can get more for less.

Every one of those sentences was derived. Not one of them had to be memorised, and none of them belongs to a particular river. Which means that when you are standing beside water nobody has ever described to you, in a month nobody has told you about, you are not out of ideas. You have the principle, and the principle does not care where you are standing.

That is what a first-principles education buys. Not more answers. Better questions, and the ability to work out the answers yourself when the fish are not where the book said they would be.

"Study to be quiet."
— Izaak Walton, the closing words of The Compleat Angler, 1653