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.