From October through the winter, the river's gravel holds next year's fish. Salmon, sea trout and brown trout all spawn in it, most of them between November and January. The eggs lie buried until the spring, and an angler who wades through them can destroy a season's production in a few steps.
What a redd is
The female turns on her side over a patch of clean gravel and beats it with her tail, lifting stones and silt and carrying them downstream. She digs a pit. The eggs are laid into it as the male releases his milt alongside. She then moves forward and digs again, and the gravel she lifts covers the eggs below.
The finished redd has two parts: a hollow where the digging began (the pot) and a mound of loose, cleaner gravel just downstream (the tail). The eggs lie inside the tail, buried from a few inches in a trout redd to a foot or so in a salmon redd.
How to recognise one
Pale gravel.
Stones cleaned of algae and silt show lighter than the surrounding bed. In low autumn water a redd stands out as a pale oval patch. Over the following weeks algae and silt dull it, but the eggs remain in the gravel until spring.
Shape and size. A salmon redd is the size of a bath or larger. A trout redd is smaller. Several redds may sit side by side.
Location. Look in the tails of pools, where the water quickens and shallows over clean gravel, and on shallow glides and runs. Sea trout and brown trout also use small tributaries and headwaters. Where gravel looks good for spawning, treat it as a redd.
Fish. Spawning fish hold close, a pair or more, often with smaller males waiting nearby. Fish on the gravel means a redd.
Why wading kills
Eggs in the gravel are fragile, most of all in the first weeks.
They are sensitive to pressure, to silt that clogs the gravel and starves them of oxygen, and to being dug up. Wading on a redd compacts the gravel and kills eggs, and it loosens stones and exposes what lies beneath.
Trampling does not leave a visible mark. The redd looks the same the following morning. The damage shows in the spring, when the fry fail to appear. The danger lasts until the fry emerge, which is March or April, so it covers the whole winter grayling season.
What to do
Look before you step.
Scan the pool tail and the shallow gravel in daylight before you enter. In low, clear water redds are easy to see.
Stay off pale gravel. If you cannot tell whether a patch is a redd, treat it as one.
Wade less, and wade at the margin. In winter, wade only as much as the fishing needs. Cast from the bank where you can. Cross where the bed is coarse cobble or bedrock, never at a pool tail.
Do not fish to spawning fish. A fish on the redd is occupied and exposed. Disturbing it wastes the spawning effort and energy it cannot spare.
Move on. Fish the deeper water above and below, where the fish are not breeding.
Kelts and spent fish
From early winter, and through the spring, you will meet kelts: fish that have spawned and are dropping back downriver.
A kelt is thin, dark and long-headed, with ragged fins and a slack belly. A well-mended kelt in early spring can look silver, but it is slim, the head looks large, and the flanks lack depth.
A kelt is a survivor. It has a chance of spawning again. Many are weak, and handling can finish them. Return a kelt at once. If one takes your fly, bring it in quickly, keep it in the water, unhook it and let it go. Do not lift it out.
Know the rules
Many rivers close to salmon fishing before or as spawning begins.
Some stay open into late autumn, and fish there are already on the gravel. Brown trout seasons on rivers generally end in late September or early October. Sea trout seasons end in the autumn on most rivers. Grayling, which spawn in spring, are fished through the winter in England and Wales until mid-March. Check the closing dates, and do not fish for species that are out of season.