Many natural areas that have the potential for attaining high ecological values have been degraded by human activities. It is often possible to at least partly restore or reconstruct the natural environment and increase a site's ecological value.
Restoration and reconstruction
Human exploitation has negatively affected many streams and rivers and their associated wildlife, for example destruction of fish spawning grounds. It is often possible to restore an aquatic environment to its former functional state by altering the physical environment, for example, by providing new pebble substrate, which reduces erosion and provides a suitable fish spawning environment.