Hydromorphology describes the physical and hydrological characteristics of rivers and its habitats including the underlying processes from which they result. Hydromorphology is a supplementary but mandatory element of WFD ecological assessment, and hydromorphological alterations were recognized as one of the most important river management issues across Europe. Hydromorphological assessments try to integrate and provide information on how far the conditions derive from pristine conditions (so-called hydromorphological reference conditions). The ICPDR Joint Danube Survey (JDS) 2 in 2007 delivered results on hydromorphological alterations for the navigable Danube River (from Kelheim (rkm 2,416) to the Danube Delta) for the very first time. A five-class assessment similar – but not equal – to the WFD ecological status classes was implemented according to European standards and methodological approaches for large rivers using the three main categories (1. channel; 2.banks; 3. floodplains).