Fish and other organisms are indicators of the ecological state. The survey of fish in the Rhine showed that, for the first time since 1970, 63 fish species again live in the Rhine. Many species, such as salmon, sea trout, sea and river lamprey have returned.
Today’s fish and invertebrate fauna, among others snails, insect larvae and mussels are far from having reached a stable balance. Due to the unnatural and monotonous state ubiquists with low demands to the ecological state dominate in the Rhine and its tributaries. With a view to improving biological diversity, rivers must become more varied and sub-natural.