This publication, a contribution to the Ecohydrology Project of the UNESCO’s International Hydrological Programme (IHP), comprises the report on the International Workshop held 14-16 October 2004 in Petronell, Austria, organized by the International Association for Danube Research (IAD) and sponsored by the UNESCO Venice Office. The workshop aimed to foster an understanding between two traditional scientific disciplines, hydrology and limnology, in view of the catchment approach and sustainable Danube River Basin management and ultimately toward the implementation of the European Water Framework Directive. It gathered 28 limnologists and hydrologists from Austria, Bulgaria, Germany, Hungary, Romania, Serbia and Montenegro, Slovakia and Switzerland.