The key in catching fish in small streams is to avoid detection.
Trout detect you in two ways. By seeing you and by "feeling you" approach through their lateral line vibration detection system.
Stay low and go slow. Stay away from the bank if you can.
The fish may see everything but they cannot recognize everything because of Snell's law of refractions which results in Snell's Window through which they see everything that is above the water level.
snell's window - Google Search
Because of Snell's Law, everything under the 10 degree line is compressed and distorted. It is their blind spot.
In a small stream, the trout cannot get very deep and this limits the size of the window. Use the rule of 6 to figure out how low you need to be. Divide your distance from the rise by 6 to figure out how "low" you need to stay. For example, at 20 feet from the trout, you need to stay under 3 feet.
If you approach from behind the fish, the width of the small stream means the tippet will likely fall into the window. If you cast above the rise, the entire tippet will hit the window. If you find that that this type of cast puts the fish down, you can then try to cast the fly just into the back of the window with the next riser. Try casting the fly 3 feet behind the rise.
If the upstream approach does not work, you will need to cast from above. The problem with this approach is that if the trout refuses the fly, you will likely spook the trout when you lift the line off of the water for the next cast. You get only one shot in a tiny stream unless the fish is in the riffles that will mask the disturbance of lifting the line.
If the stream is wide enough to get the line out of the fish's window, take the line to the side of the stream furthest from the rise and slowly strip it back until it is well away from the rise before lifting the fly off the water.