Building on existing data, this task reviewed and analysed the available knowledge on biological responses to hydromorphological degradation and restoration. The effects of hydromorphological changes on aquatic plants, macroinvertebrates and fish have been analysed on the one hand with regard to specific requirements of species as potential sensitive indicators and on the other, with regard to limitations of species due to hydromorphological forces aiming to derive thresholds and boundaries of impacts as well as guidelines for rehabilitation.

Building on existing data this task reviewed and analysed the available knowledge on biological responses to hydromorphological degradation and restoration. It went beyond recent projects by especially focusing on the specifics of changes, structures or features determined by hydromorphology and their effects on biota. The main objective was reviewing and compiling the available scientific and grey literature, data and information to analyse the effects of hydromorphological variables and processes on the mandatory biological quality elements of the Water Framework Directive: macrophytes, macroinvertebrates, and fish. Further objectives comprised

i) conceptual considerations and analyses to identify key hydromorphological structures and biological responses to hydromorphological degradation and restoration

ii) identifying principal cause-effect chains for hydromorphology-biota interactions to be used in developing assessment and restoration evaluation tools and to add to the efficiency of measures

iii) compiling guidance on relevant information.

Summing up, the effects of hydromorphological changes on aquatic plants, macroinvertebrates and fish have been analysed on the one hand with regard to specific requirements of species as potential sensitive indicators and on the other, with regard to limitations of species due to hydromorphological forces aiming to derive thresholds and boundaries of impacts as well as guidelines for rehabilitation. In addition, potential indicators for the hydromorphological integrity of entire river zones were suggested.