Have you ever stood by a river and noticed the current? In some spots the water seems fast, slow, some over rocks or wood, a little bit white water, a bit that looks as if it’s not moving at all, and then you might see some that looks as if it’s headed in the exact opposite direction. All of this is natural, and so is everything that floats through it.
This is your goal at all times: present your fly in the most natural way you possibly can. Sometimes that is easy for you, stand downstream, cast upstream past your given target and then let the fly drift back to you stripping a bit of line as the fly progresses on its drift. Other times an angler must stay out of the water, either to keep that stretch without disturbance or because the conditions do not promote safe wading. This is where mending comes in.
We, as anglers, are always looking for the best drift of our fly as possible. The best drift is the most natural drift and the enemy of this is drag. Drag is when the fly drifts too slowly, or in the wrong direction, or even too quickly through the water, any movement of your fly that is inconsistent with the flow of the current is drag.
Mending is using your rod to flip your fly line upstream to slow down your fly so it moves at the same speed as the water. Imagine the most common scenario - casting slightly upstream and landing your fly on top of the water near the opposite bank.The current in the middle of the stream moves faster than at the banks. This faster moving current starts to pull the line laying across the middle of the stream. As this happens your line in the faster current will drift ahead of your fly and start to drag it through the water at an unnatural speed.
When you mend you simply flip some line upstream of your fly. You want to start your drift with the line in the fast water upstream of the fly in the slower water. As your fly goes through it's drift the line laying across the middle of the stream with eventually pass by your slower moving fly. But until it passes your fly will have a brief period where the fly drifts at the exact speed of the current. A second mend will reset the line and allow the fly to continue a natural looking drift a little farther.
The rod motion to make a mend is just a quick circular flip of the rod tip in the direction you want to place the line. An addition push of the rod tip away from you as you make the circle can help make a bigger mend.
Don’t let the simplicity of mending fool you. It is arguably the most important skill in fly fishing. You may end up mending three to four times as much as you cast in a given day. An angler can also mend mistakes out of a cast, if you master one skill make it this one.