Approaching Unseen

Picture an angler spending a quarter of an hour choosing a fly for a trout that left the pool before the box was opened. He walked up to the bank upright, with the evening sun behind him, and stood on the skyline to tie the knot. The fish, lying in a foot of water under the far alders, simply slid away into the roots. Nothing was wrong with the fly. Most of the trout we fail to catch are lost in this way, minutes before the first cast, and we never know it.

The window

Light bends as it passes from air into water. The result, for anything looking up from below, is that the whole world above the surface is squeezed into a circle directly overhead. This is called Snell’s window, and it corresponds to a cone of roughly 97 degrees with its point at the fish’s eye. Outside the circle the underside of the surface acts as a mirror, reflecting the river bed.

Two consequences matter to the angler. First, the size of the window depends on depth. Its diameter is a little over twice the depth of the fish’s eye, so a trout lying 30 cm down looks out through a circle less than 70 cm across, while one at a metre has a window more than two metres wide. Shallow-lying fish see a fly late and at close range. Deep ones have more warning of everything.

Second, the full sweep from one horizon to the other is packed into that circle. The sky fills the centre, and the bank world of trees, cattle and anglers is compressed into a thin distorted ring around the rim. An object low to the horizon appears squashed and dim at the very edge of the window. An object standing tall rises out of that rim towards the clear middle. This is the whole reason for keeping low: an angler who stays within about ten degrees of the horizon, as the fish sees it, remains in the blurred margin.

The blind zone

A trout’s eyes are set on the sides of its head, which gives it a very wide field of view with one narrow gap: a wedge directly behind the tail, of around 30 degrees. Because a trout holds station facing into the current, that wedge points downstream. Approaching from below, moving up the river, puts you in the only direction the fish cannot watch. It is not a guarantee. A fish in a back eddy faces the other way, and any trout swings from side to side as it feeds. But as a starting point it is the best there is.

The fish cannot count your flies. It can see your hat against the sky.

What gives you away

• Skyline. A figure against open sky is seen from far off. Keep a background behind you, such as a hedge, a tree trunk or a high bank, and approach where one exists. Kneel where there is none.
• Shadow. A shadow crossing the water means a heron to a trout. Know where the sun is before you reach the river and fish from the bank that throws your shadow behind you. This matters most early and late, when shadows are long.
• Vibration. Fish feel low-frequency disturbance through the lateral line. A heavy tread on a soft or undercut bank travels straight into the water. Walk softly, heel down first, and never jump down a bank.
• Movement. Sudden motion alarms fish far more than shape. A slow hand is nearly invisible. Raise the rod, change flies and turn your head at half the speed that feels natural.
• Rod flash. A glossy rod waved in sunshine sends flashes across the pool. Cut false casts to two, make them off to one side of the fish, and cast side-arm under the level of the bank where you can.
• Colour. Olive, tan, grey and brown, chosen to match what stands behind you. White shirts, pale hats and shiny tools on the waistcoat all show.

A way of arriving

1. Stop 15–20 metres short of the water and look. Find the rises, the likely lies, the sun and the available cover before going any nearer.
2. Choose your position below the fish and to one side, with something behind you. Decide where the back cast will go.
3. Cover the last ten metres slowly and bent double, and the last three on your knees. Keep the rod pointing behind you, low.
4. Settle, and wait a full two minutes before doing anything. If the fish is still rising at the same rhythm, you have arrived unseen.
5. Lengthen line over the grass or well away from the fish, then make the first cast the best one.

After a mistake

Everyone stumbles, snags a thistle or lets the line fall in a heap. What you do next decides the matter. Freeze. Do not retreat, crouch suddenly or cast again to make amends, because each of those is one more movement. Stay still for five minutes, ten if the water is low and clear, and watch. Very often the fish drifts back onto its lie and after a while tips up for a fly. Wait for three unhurried rises before you move a hand.

Kneeling in wet grass with nothing happening is fishing too. Herons know it.

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