Use a reach mend to establish the line layout you want before the line and leader land — most often in moving water, where the goal is a drag-free drift. The reach is not tied to one direction: it can go upstream or downstream as the situation requires.

What the upstream version buys you:

• A longer drag-free drift. With the line and leader upstream of the fly, the current reaches them first, so the fly drifts without being dragged.
• No disturbance on the water. The mend is made before the line lands, so nothing splashes the water the fish is holding in.
• The layout is set before the current has a say. The line is mended before the water starts pushing it, so you get the layout you chose.
• A shorter, softer delivery. Without slipping line the reach shortens the cast — ideal for dry-fly presentation at short range.

Be clear about what moves: the line and leader, not the fly. The reach does not drop the fly into a feeding lane while it is still in the air; the fly lands where the cast put it, and the mend sets the line for the drift that follows. With too little line it can also pull the fly off target.

Source

From the CI Study Guide (2025) (PDF), Task 4 — reach mend with and without slip and the reach-mend lesson plan (Appendix C); terms from the FFI Fly Casting Definitions (Aerial Mends, Slack Line Presentations).