This volume offers a comprehensive review of the chemical, biological and hydromorphological quality of the Danube. The first part examines the chemical pollution of surface waters, focusing on organic compounds (with special emphasis given to EU WFD priority substances and Danube River Basin specific pollutants), heavy metals and nutrients. Attention is also given to pollution of groundwater and drinking water resources by hazardous substances and to radioactivity in the Danube. The second part highlights the biology and hydromorphology of the Danube. It focuses on benthic macroinvertebrates, phytobenthos, macrophytes, fish, phytoplankton as well as microbiology, with chapters dedicated to gaps and uncertainties in the ecological status assessment and to invasive alien species. Further chapters dealing with the hydromorphology, sediment management and isotope hydrology complete the overall picture of the status of the Danube.