2. Put the sun behind you, without putting your shadow in front of you. Do that, and the river lights up so you can see better.
3. Look through the water column,** not only at the bottom or the surface of the river. Looking through the water allows you to pick up motions that reveal a fish's presence.
4. You're looking for a star, not the whole night sky**. In other words, focus your gaze, and realize that what you are really looking for is a fin, or a shadow, or a glint reflecting off scales. You don't see a whole fish (usually) until you learn how to spot part of a fish.