For a hundred years potassium salts are mined industrially in the Werra catchment area. There is pollution of the Werra and Weser with salt ions (most of all chloride, magnesium and potassium, but also sulphate, sodium and calcium) for several hundred kilometers caused by the production wastewater of the local potash mining.

Compared to the normal status increased salt contents and changed ion composition, lead to negative affects to flora and fauna, but also to the diverging human water use (for example drinking water and irrigation). However the fluctuations of concentration are a problem too.

After the German reunification a technical salt reduction concept for Werra and Weser was concluded in 1992 and implemented in 1999. The success can be seen at the Gerstungen monitoring station indicated by the mean daily chloride levels.

An overview of the salt concentrations of the whole Weser river basin shows significant hotspots at Werra and Upper Weser. In spite of advancing dilution along the river, the impact of salt pollution can be observed down to the end of the Middle Weser.

Data chloride and other ions in the (in German)