Trout hold where three conditions overlap: food delivered, slow water to sit in, and cover from predators. Reading water is the skill of finding those overlaps before you cast, and it usually matters more than fly choice.

The four places fish live

• Seams. Where fast water meets slow. The fish sits in the slow side and eats what the fast side brings. Fish the edge, not the middle.
• Behind structure. Boulders, log jams, bridge pilings. The pocket directly behind a rock is slower than the water either side, and it is where the biggest fish in a riffle usually sits.
• Ledges and drop-offs. A depth change concentrates fish because it gives them deep water to retreat into and shallow water to feed in.
• Foam lines and bubble trails. These mark a current seam on the surface. Food collects there. Follow the foam.

Read the surface, then the depth

The surface tells you where the currents are; the water colour and chop tell you where the depth changes. Look for:

• Nervous water — a small boil or a hump in the surface that does not repeat with the current. Usually a fish moving.
• Colour changes — a darker patch often means deeper water or a different bottom.
• Riffle-glades — the slow water beside a riffle is the most reliable dry-fly lie on the river.

Work upstream, and fish the close water first

Approach from below so you are behind the fish’s window, and cover the water nearest you before the water further out. The fish you spook with your first cast is usually the closest one — the one you did not see because you were looking at the far bank.

For how presentation changes with each of these lies, see What is drag, and how do I beat it? and What is a dead drift?.