Clean rivers are especially important as habitats for Brook Trout and other salmonids.
Most rivers in the Northeast were formed many years ago by glaciers and continue to be shaped and carved by moving water. In New England many river valleys are U-shaped, having been carved out by glaciers. River valleys such as those in the southern and western United States tend to be more V-shaped as a result of having been cut by water rather than having been carved by glaciers.
As rivers age they meander, or turn from side to side, as water alternately erodes the streambank on one side and deposits sediments on the opposite side.
The dynamics of moving water create small specialized habitats called microhabitats within rivers. Deep undercuts of the stream bank form when water erodes one side of a bend in the river, then another. Sometimes fish will rest in these undercuts away from the fast-flowing current of the main channel. Water flowing over rocks and cobbles creates riffles, runs and pools. Riffles attract small fish because they offer places to hide between rocks and an abundance of aquatic insect larvae. Larval aquatic insects and other macroinvertebrates often secure themselves to rocks at the boundary layer, a layer of slowly moving water between the rock and the swiftly moving water above it. Macroinvertebrates also cling to the undersides of rocks. A snail might find a home or a fish may take refuge in the calm eddies that form on the downstream sides of rocks. Fish will also take advantage of deep still pools in rivers for rest and protection.
Streamside vegetation is responsible for many other riverine microhabitats. Large streamside trees perform many wetland functions when they are standing and provide valuable protection and pools when they fall into a stream. Willows, cattails, wild celery, arrowhead, prickrel weed, tussock sedge and other species growing along the edges also serve as habitat for amphibious, terrestrial and aquatic organisms. Farther up the bank, the trees, shrubs and vegetation provide very important protected areas for terrestrial wildlife. Sometimes these strips of trees and plants along rivers are called riparian corridors. They allow animals to access water and to migrate within a continuous stretch of habitat. Eliminating riparian corridors fragments and threatens plant and wildlife habitats.
Preserving habitat is one very good way of preserving species.
If a problem within a habitat affects one plant, animal or micro-organism, it is likely to affect several others because all organisms within an ecosystem are interrelated.