The flow will also dictate how the sediment is deposited, which in
turn contributes to the type of habitat
available to different types of organisms. Three types of bedforms
provide excellent "living" space, including mud, riffles, and
pools. The accumulation of fine-grained sediments (mud) in quiet
rivers can influence growth for small invertebrates and fish eggs. The
mud represents a "cushion", and if disturbed because of
increased movement of water, can cause damage to the organisms that live
Riffles are relatively shallow portions of a river with a change in
elevation where water cascades over cobbles or boulders along its path.
The fast-moving water allows gas in the atmosphere to mix with the
water, therefore increasing the dissolved oxygen that enters the water
system. Behind the rocks are areas that debris can build up and act as a
habitat for fly larvae and other small invertebrates.
Pools of water are areas that are deeper. When water reaches a pool
the velocity of the water slows down, making it an excellent resting
place for fish.