In moving water, fish face upstream. Before planning an approach take into account the fish’s location in terms of its exact position and depth. Its depth determines the window size through which a fish views the outside world. A fish holding close to the surface has a much smaller window to see through than a deeply holding fish.
Approaching a shallow fish is easier than a deep one. The smaller the window, the less likely a fish can see you. Try hiding from the fish by staying outside of its vision window.
Fish are overly cautious to vibrations sensed by their lateral lines. However, shallow-holding fish may be more alert because they are more vulnerable to predators and will streak for cover at the slightest provocation.