Nymphing Technique.
Normally I fish nymphs with short casts either directly up
stream or slightly to the side but still towards the current. Short casts, I've
found, gives me all the control and contact I can wish for. These short casts
are always combined with reach-mending, as this is by far the best technique to
avoid having the fly line land over the fish.
I try to use reach mending in all my fishing at streams, since this technique
gives me a tool to present the fly in the best possible way without having to
mend with the line already in the water.
However, at times the short casts do not suffice, mostly
because the river is quite large and/or wading impossible. So when reaching fish
in larger rivers it's necessary to cast sideways into the current. In doing so I
always try to create a little curve on the line by techniques of mending, so
that if and when dragging occurs it's directed straight downstream.

This can be done in an easier way than on the picture above, only I don't know
how to describe this.
After mending I will have a curve that keeps the nymph drifting straight
downstream whether my line pulls on it or not. By widening this curve you can
affect the nymph in a manner that makes it move slightly faster than the current
and as such not sink as fast. At the end of each drift when the nymph starts to
rise towards the surface, due to the pull of the line, I try to wiggle the rod
tip ;-) somewhat, so that the nymph gives a lively impression.

Realize that this technique, while it actually works, isn’t a preferred method
if you want to fish your nymph in an absolute dead drift. The water on the
surface moves somewhat faster than the water at the bottom of the stream, and as
a consequence a drag free strike indicator means that your nymph is dragging.
The optimal situation would in this case be to have an indicator that drags
against the stream, pulled by the weighted nymph. In order to achieve an
absolute dead drift you would have to mend upwards in the stream to avoid the
fly line pulling on your nymph, i.e. the exact opposite to the above mentioned
technique.
So, what triggers a strike whilst nymph fishing? Of course some of the obvious
reasons are that a strike indicator disappears from the surface or that it just
stops dead in the stream, but there are also more subtle indications. One
indication that I started to use when fishing very fast water with the above
illustrated nymphing technique was that although I couldn't always see the
indicator or line tip it was easy to spot the point where the line curved
upstream. This point of the curve also reacts to a fish striking the nymph by
either slowing down or at times even as a jerk upstream.
I use a 10 feet #5 for nymphing in big rivers because it gives me more control
but also because it is fast when striking, something needed when there's a lot
of line out on the water. I stopped using braided / weighted leaders more than
ten years ago since these seem to affect the drift to much and they are very
irritating to cast with. Instead I prefer long, fairly thin leaders with
weighted nymphs.
--
Tight lines!
/ Roger