The structure of water bodies that is the nature of the river bed, the banks and floodplains has been immensely changed throughout the entire Rhine river district. During the past 100 years, almost the all of the Rhine and its tributaries – above all Neckar, Main and Moselle - have been dammed and trained for purposes of navigation, hydroelectric power generation and flood control. Dikes separate the floodplains from the river. All this has serious consequences for the river ecosystem. In order to improve the ecological state, water bodies must be more nature near and free fish migration must be re-established, e.g. with the help of fish ladders.