Current state-of-the-art research identifies Europe’s water bodies and resources influenced by a complex mixture of stressors. Understanding how stressors interfere and impact biological and chemical status of aquatic system is identified as main challenge for shaping future environmental policies. To meet the challenge multiple stressors effects should be understood equally from stressor and receptor side. Accordingly, UNDERSTANDOR aims at advancing our knowledge on stressor and receptor properties in multi-stressed aquatic environments. In particular, on “stressor’s side” the project will further develop and apply some of the cutting edge computational chemistry methods and multifactorial photodegradation studies to improve our understanding of ensemble interactions of emerging contaminants (ECs). Special emphasis will be put on carbon based nanomaterials and their interactions with other xenobiotics during adsorption and photodegradation. From a “receptor’s side” the project will provide a multidisciplinary perspective of molecular responses and mechanisms resulting from multiple stress events (e.g. ECs, temperature, drought). The project proposes use of Experimental Stream Facility (a unique European facility) and mesocosm experiments that will permit temporal “omics” profiling of biofilm community and aquatic macroinvertebrates at environmentally relevant (long-term low-dose) multiple stress events. Obtained profiles will enable reconstruction of time points in gene-protein-metabolite dynamics of biofilm and macroinvertebrates under stress conditions. By assembling a multidisciplinary team of four European and one non-European scientific institution with unique combination of skills and expertise, a critical mass of experience and knowledge will be mobilized to carry out the project activities. Accordingly, we expect that the results produced by this innovative research plan will have substantial impact on the field of inland water research.