Trout don't hold in featureless water if they have a choice. Structure gives them a current break (so they're not constantly working), overhead protection (from osprey, otters, and anglers), and a feeding ambush point.
Categories:
- In-water structure: boulders, root wads, downed trees, ledges, deep cuts.
- Bank structure: undercuts, overhanging foliage, dock pilings, riprap.
- Depth structure: drop-offs, mid-stream channels, the deep slot at the head of a pool.
Always cast to structure, not directly at it. Let the fly drift past, or land just upstream so the drift covers the holding zone.