Set the hook on any flash subtle movement on the fly line twitch of the rod tip or any other sixth sense that just felt fishy.
High stick nymphing without indicator.
When nymphing without an indicator high sticking or czech nymphing for example you are relying on feel to detect strikes.
Sight fishing to spooky fish in shallow water is best done without a bulky indicator because the splash of an indicator often scares trout but there are other places you.
As always when nymphing setting the hook on anything suspicious will inevitably lead to more fish.
Galloup says he developed the high stick drifter with a lightweight tip to reduce fatigue from holding the rod high during long periods of technical nymphing with or without indicators and to provide extra sensitivity for better strike detection.
With czech nymphing there is no fly line on the water.
I learned to fish nymphs without the benefit of strike indicators they have only been widely used since about 1980 and i still love to fish that way if conditions allow.
In this case it is even more important to have as little line as possible on the water.