In addition to the direct benefits to fish listed by That Idiot, streamside vegetation provides some crucial indirect benefits.
One indirect benefit is falling leaves. The leaves of streamside vegetation fall into the water and decay. Decaying leaves feed benthic macroinvertebrates. These include aquatic worms, snails, clams, crayfish, and the aquatic lifestages (larvae and nymphs) of insects like dragonflies, craneflies, midges, etc. If the names of any of those organisms sounds familiar, it's probably because you have a fishing lure that imitates one or more of them. Fish eat benthic macroinvertebrates. Without benthic macroinvertebrates, you don't have fish.
Streamside vegetation also prevents erosion. If the streambanks now have bare, exposed dirt, that dirt is eroding into the stream. Dirt in the water increases turbidity and decreases water quality, both of which are bad for fish as well as benthic macroinvertebrates. When dirt falls on the bottom of the stream, it fills in the spaces between rocks where many benthic macroinvertebrates live, displacing or smothering them.
Streamside vegetation slows overland flow of rainwater after a storm. It helps the rainwater to seep into the ground instead of going directly into the stream. With the lack of streamside vegetation along this section of the stream, any chemicals carried by that water (eg, oil or salt from the nearby road) go directly into the stream. This decreases water quality, harming both the fish and their food supply.
For more information about the benefits of streamside vegetation, look for information about Riparian Buffer Zones. This document has some good information: Riparian Buffer Zones: Functions and Recommended Widths