Many new micro-organisms living in and on the bottom of the Rhine have immigrated from other waters or been introduced via canals, such as the Main-Danube canal opened in 1992.
The basket clam which has its origin in Asiatic and African regions first appeared in the Lower Rhine in 1988, reached Basel in 1994 and today belongs to the most common mussel species in the Rhine. Exotic fish also feel at home in the Rhine. The tubenose goby, for example, immigrated to the Rhine via the Main-Danube canal (see ICPR report no. 208) .
The fact that species from Asia or the Caspian Sea also thrive in the Rhine is among others also due to the fact that, during the last century, conditions of life in and along the Rhine have changed. Intensive use of water in households and industry have increased both water temperature and salinity. Habitats have also changed with respect to flow velocity and surface conditions. Some of the original species of the Rhine today only find the habitats they require in the floodplain and in Rhine branches, while the main stream is mainly colonized by undemanding ubiquists and immigrating species. Above all, euryoecious „immigrants“ with a high rate of reproduction are able to prevail over established species.
that the share of immigrated “new species” may, along certain sections of the Rhine, reach up to 90 per cent?