Nymph fishing techniques, in general and more specifically strike indicators, will generate as much heated discussion among fly fishers as any topic: to use an indicator or not to use one, which type of indicator to use, and where to place the indicator on the leader. Every nympher will have a different opinion on these nymph fishing nuances. Like most things in life, the best choices are situational.
There are those, often curmudgeonly individuals, who refuse to use an indicator and speak of a Zen like feeling for when there is a take. I’m about as curmudgeonly as they come, but have apparently have never reached that Zen like state when I never need a strike indicator.
Under most nymphing situations an indicator is called for. But there is one situation where an indicator may not be necessary or even the right thing at all, short line or high stick nymphing. In this situation, where your line is hanging directly below the tip of your rod, you can get a drag-free drift by moving the tip of your rod along the seam you want to fish your nymph in. Since the nymph will be directly below your rod tip you can be sure of where the nymph is drifting. And being “tight to the nymph” the take will be transmitted to you via the rod.
In situations other than ‘high sticking” an indicator is basically essential for an acceptable drift. With an indicator your nymph will hang directly below and perpendicular to the water surface. Without the indicator the cross stream currents will cause your line to swing and pull your nymph out of your drift line up toward the surface and toward you. That is not to say that simply putting on an indicator will eliminate a swing. You still have to mend to keep the line at as close to a right angle to the indicator as possible and the nymph and indicator in the current seam you want to fish.
In choosing an indicator, look for these four things: floatability, castability, color and. easy position adjustment. By floatability I mean an indicator that has enough buoyancy to be able to support the weight of the nymph you are fishing. Select the smallest indicator that will do the job for the flow conditions. In smooth water and for spooky fish a big indicator will often put fish down. In heavy water you generally will need a bigger indicator for the same weight fly. Remember, the smaller the better
Nymph fishing does not require artful casting. I’m sure you have heard it described as “Chuck and Duck!” By castability I’m referring to the additional wind resistance and weight. This is especially true with the yarn type indicators. Pick an indicator that doesn't interfere with your casting. As with floatability, the smaller the better.
Color? Most indicators tend to be a shade of florescent pink or light orange with a few in a florescent line green or plain white. I learned about color from my time working as a water scientist. We used florescent dye to study stream mixing zones and determine “time of travel”. I remember standing on a bridge with a co-worker and said “Here come the leading edge”. He looked at me like I was joking with him. We had used Rhodamine WT, a fluorescent pink dye and he couldn’t see it. On the other hand if we used Fluorescein Dye, a florescent green dye, I couldn’t see it. So what about white? If you are nymphing in water with a lot of foam and low light conditions a white indicator often gets lost. That is especially true with small indicators.
Perhaps even more important than the fly your chose of the nymph to use, is making sure that your choice gets down to where the fish are. As water depths change and you need to adjust the depth of your nymph, an indicator that can be moved up or down easily is what you want. My experience is that the various press on foam or indicator putties don’t work well and the residue left behind on your leader tends to inhibit sinking.
Nymphing on streams were the depth doesn’t change that much from one location to location, the need to be able to re-position your indicator on the leader isn’t all that critical. This is often the case on small streams or pocket water areas. In these situation I’ll generally go with a high floating dry fly such as an Elk Hair Caddis or a Stimulator as an indicator. I just tie my nymph on as a dropper at about 1.5 times the depth of the water and leave it there.
So what is my indicator of choice? For me it is a pink Thingamabobber. I buy the smallest size, ½ inch. If I need more buoyancy for a big Mohair leech in heavy water I just add a second one.