Neobiota" is the term used to describe immigrant animal and plant species that have settled in our country. Species are called "invasive" when they become a problem for native nature. But let's start at the beginning: The Rhine was "straightened" back in the 19th century for the purposes of navigation and shortened by a total of 81 kilometers (!). Since then, it has served as a federal waterway for ships from many countries, often carrying foreign animal and plant species from all corners of the world. Many plant seeds also spread over long distances by floating along rivers.

The Rhine and its banks are therefore full of "newcomers". So much so that there are now more fish species in the Rhine than there were originally - sometimes unfortunately to the detriment of the original native species. One species of fish, the river goby (Neogobius fluviatilis), has been spreading particularly rapidly in recent years and is becoming a major problem as it eats the eggs of other fish. The introduced subspecies of the Asian basket mussel (Corbicula fluminea, Corbicula fluminalis), which can also be found everywhere on the banks of the Rhine, are food for many waterfowl and mammals. In Asia, it is also on the menu for humans.

The Atlantic salmon (Salmo salar), on the other hand, became extinct in the 1950s. With the help of humans, salmon of various origins are being reintroduced to Germany at great expense and have been returning to the River Sieg and other tributaries via the Rhine for some time now.

Willow trees are amazing in several ways: they are very hardy, extremely fast-growing, ecologically very important and not very picky when it comes to choosing a partner... but first things first: Many willow species typically line the banks of rivers; they are so-called floodplain dwellers. Here they defy every flood, the elastic branches bend in the water and the roots can withstand being submerged for a while.

If a branch is torn loose, it can immediately regain a foothold on open ground, for example where it washes up, and quickly grows into a new willow tree or shrub. People take advantage of its flexibility and vigor: they use willow branches to build baskets, fences, gazebos and other "living structures" in their gardens.

With their lush flowering in early spring, when not much else is in bloom, willows are a very important insect food. Incidentally, both male and female willows flower as catkins - the difference can only be seen on closer inspection. And the changing partners? There are around 300 willow species in our latitudes. And they are able to mingle with each other. If insects carry the pollen of another willow species, a new species of "mixed willow" can develop, a so-called hybrid. Strictly speaking, it is almost impossible to determine the exact species of a willow tree.

Unfortunately, people keep releasing fish, turtles and amphibians into rivers and lakes - according to the motto "out of sight, out of mind!". Some species cause great damage to the local environment through their aggressive behavior and diseases. Therefore, if you are a true animal lover, leave exotic species in the aquarium and do not "dispose of" them in the wild.