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. Most rely on the water to regulate their body temperature. Water enables them to move and migrate.
Water is also very important for spawning and successful reproduction.
Let's consider each of these points. Fish need water to breathe. Salmonids are very active fish and they require lots of oxygen. They need water that is nearly saturated with oxygen to survive. Oxygen levels also vary from place to place and time to time.