Gewässerkennzahl
The Gewässerkennzahl ( GKZ , rarely GWK or GEWKZ ) or "waterbody index number/waterbody number" is an identifier with which all watercourses in Germany are numbered , together with their catchments and precipitation areas . 
<triplet> Gewässerkennzahl <subj> waterbody number <obj> instance of <subj> Germany <obj> country