Dry-fly fishing is the visible, exciting version: a floating fly, a rise, a strike. Nymphing is the effective version: a weighted fly fished below the surface where trout do the great majority of their feeding. Learning both is not optional if you want to catch fish in all conditions.

Choose a dry fly when

• You see rises — fish breaking the surface, or the small boil of a fish taking an emerger just under it.
• Insects are on the water: a hatch is coming off, spinners are falling, or terrestrials are being blown in.
• The water is shallow, slow and clear enough that a fish will move up for a fly.
• You need a visual take: beginners learn faster watching the fly.

Choose a nymph when

• Nothing is showing on the surface. On most rivers, most days, this is the answer.
• The water is cold, high or fast — trout hold deep and conserve energy.
• Fish are visibly feeding but not on top: flashing, or moving sideways without breaking the surface.
• You are fishing a deep pool, a tailwater, or pocket water you cannot cover with a drag-free float.

The honest ranking

If you want to catch fish, learn to nymph first: an indicator rig or a tight-line approach with a hare’s ear and a pheasant tail will out-fish a dry fly on the majority of days. Then learn the dry fly properly, because on the days it works it is the best fishing there is — and because a large part of the CI teaching tasks are taught and examined on the surface where the examiner can see the loop.

Fish both in the same run: nymph the deep seam, then fish a dry over the tail-out. Covering a pool in the right order beats changing flies.