When looking for rising trout I watch the flat water river sections first. That’s where they are easiest to spot. If there is no activity then I search the riffles. Trout in this location are much more challenging to find due to the water being broken and faster. Throw in river glare and spotting can be especially daunting. So I focus on very shallow sections. Often water just six inches to one foot depth. Large trout feeding sub-surface in very skinny water occasionally break the surface, and therefore make noise and notify you that they are around. Sometimes it’s barely perceptible above the constant sound of the flowing water. But you get good at hearing it. You just have to stay in one place for a while and listen. Large trout in the shallow riffles also push or displace water as they intercept nymphs and emergers, and occasionally rise for a dun. Their feeding can disturb and slightly change the riffle surface pattern. Again, almost imperceptible. You have to concentrate and watch the water to notice. It’s all subtle. You have to observe and concentrate…kind of the key to learning and becoming a better fly angler or really a better anything.
The trout in these ultra-shallow areas can often be enticed to take a dry-fly or a dangling emerger pattern. On my broad local tailwater river fish hooked in the riffles sometimes have to sprint 40, 50, 60 yards before they get to the main deeper flow. Thrilling first runs. Thrilling stuff.
Of course an angler can fish the riffles blind by swinging a streamer or prospect with a nymph below a strike indicator, or below a big dry-fly. These can be effective ways to cover these bumpy areas and catch trout.
I find spotting them first before casting, however, requires all of your senses and observation skills, and the practice further develops and hones your angling abilities. A decade ago I would have walked by the riffle stretch I fished this past Sunday afternoon and spotted nothing. It’s the same now as it was then…but now I see (and hear) more.