On the river I have been fishing, there is a section where the road was rerouted, and another where a dam was torn out. In both cases, those sections of river have fewer bushes and trees and the grass is only slowly growing back.
It makes it easier for flyfishing because my chances of getting caught up on vegetation is way less, but would the lack of shore vegetation mean there are fewer fish in those sections of river?
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
Lack of vegetation along the banks will have a number of effects, each of which can affect fish populations.
Vegetation will shade the water. This will reduce water temperatures which is typically good for fish. The shade can also provide cover for fish in the stream and give them a greater sense of security.
Vegetation along the banks will affect what kinds of terrestrial insects wind up in the water. Terrestrial insect fly patterns can be very productive for larger fish in areas where they have grown used to grasshoppers falling in the water, for instance. Their willingness to go after such patterns will be greater in areas where they see them often (vegetated banks) and less so in areas where there is no such vegetation and the fish rarely see such food.
Vegetation can provide some protection from the wind, which could affect your presentation. More importantly, though, is that it can provide something to hide behind as you make your approach to the stream. So even if there isn't much difference in the number of fish between vegetated and non-vegetated sections, your approach will more likely go unnoticed if you are sneaking up behind vegetation. Presenting to naive fish is always preferable to presenting to wary fish.
I agree with the other guys on the importance of aquatic plants and fish life. However, I would like to present another point: too much weed does not increase fish number/quality in the sense that over flowing weed will take away fish's space, oxygen and vision to lure.
Got the first point from a local tackle shop owner. His argument is that in the early summer month, weeds will grow fast and thick, make it impossible for even panfish to move around. He would wait until lily pads to grow and kill under water weeds by blocking the sun and then he would targeting bass that hides under the newly available space.
Abnormal weed and algae growth caused by global warming and over nutrition can lead to fish kill as documented in many places. Also, fish cannot see your lure when they are behind carpets of water plant.
These corresponds to the find weedline in boat fishing. I do hope the road construction did not destroy a potential spawning ground for fish.
