Artificial changes along the Trent, due to navigation, farming, mineral extraction and drainage works, mean that much of the riparian landscape has been altered, reducing the amount of natural habitat. The river channel links the remaining, but fragmented wetland areas and nature reserves, providing a refuge for native and migrant species. These include wildfowl and wading birds that use the Trent Valley as a migration corridor, with the river also being used as a wildlife route by mammals such as otters and non-native American mink. It forms part of the Severn-Trent flyway, a route used by migratory birds to cross Great Britain.