When it comes to reading river water,I`m surprised that no one mentioned using polaroid glasses to see through the glare and find fish. Note where they are lying and the current conditions . This will give you confidence when you see similar conditions but cannot see fish.
As many pointed out reading water is a lifelong study.
Always recognize the decline in current speed from surface to bottom. The rougher the bottom the greater the current gradient. The closer to the bank the greater the friction and slowing of the current.
Fish cannot continuously swim in water with a current speed of over 2 knots.