There are a few basic visual clues one can learn to observe about streams in order to narrow the window of where fish are likely holding, especially on big rivers where fish could be anywhere; especially if you don't know how to dissect large parcels of water into smaller subsections. One of the most obvious and often overlooked indicators of likely fish locations are the bubble lines or bubble zones. Bubble lines occur where the current gathers together usually as a result of some instream structure funneling the surface bubbles into predictable locations which also funnels food into a small area making feeding easier for fish, thus expending fewer calories in an effort to feed. Instead of having to swim all over the place looking for food, a fish can hold in a preferred spot where the food is funneled directly to them. Current seams can also define the location of a bubble line or at least prove a location that can also funnel food into a narrow band. Though typically a bubble line is caused by underwater structure. Structure that gives fish a safe location in which to hold and feed. Usually, you will find current seams and bubble lines very near each other,
In the images below, I illustrate some of the most obvious instances of water that contains bubble lines, current seams and structure. If you stumble upon a small section of water that contains all three, take a moment to analyze what you are looking at. Chances are there may be a feeding fish.
In figure 1. You can see several prime structures you should look for when searching streams for likely trout holding water. There is an obvious current seam defining the slow and fast water, obvious underwater structure fish can use to hide near and a bubble line funneling food into the best possible holding spot. Can you identify where the fish should be in this picture?