Shredders are most abundant in streams heavily shaded by deciduous trees. Collectors are often found in extremely high densities below the outlets of lakes because they collect lake plankton. Scrapers are most abundant in sunlit sections of the streams. They are often dominant in streams too wide to be covered with the canopy of trees. As you can see, the different types of insects, like fish and all other living things, prefer certain habitats.
Aquatic insects are the most important food of most stream fish.
These insects may be larvae on the bottoms of streams or drifting in the currents. They may also be adults flying above the stream or landing on the water or vegetation near the water. Therefore, a good insect population in a stream is very important to trout and salmon. Water Fish rely on water for many things, therefore, it must not be polluted. Fish need water to breathe.