A riffle is a stretch of stream where the surface breaks over rocks — fast water, broken into tiny waves and bubbles. Two things happen here that fish care about.
First, the broken surface oxygenates the water. Fish breathe more easily in a riffle than in a slow flat pool, especially when the water warms up in summer.
Second, the fast water dislodges insects and washes them downstream. Fish don't sit in the riffle — the current is too strong to hold position efficiently — but they sit on the seam where the riffle slows into a flat or pool, picking off whatever drifts past.
Look for:
- The tail of the riffle, where the broken water flattens out. Fish hold here.
- Soft spots behind boulders inside the riffle itself — small pockets of slack water surrounded by fast current.
- Foam lines below the riffle. Foam tracks the same path floating insects take.
A clean cast lands above the seam and drifts through it without drag.