www.freshwaterecology.info – An online tool that unifies, standardises and codifies more than 20,000 European freshwater organisms and their ecological preferences

•Ecological preferences of freshwater species were collated into an online database.•654 fishes, 8586 invertebrates, 1083 macrophytes, 8868 diatoms, and 1976 phytoplankton.•106 bio-/ecological parameters.•Various options and tools for finding and tracing back information.•Applicable for research, monitoring, assessment, restoration, and modelling. Species’ ecological preferences are progressively important for understanding distribution patterns, for conserving biodiversity or for assessing and evaluating the status of freshwater ecosystems. Comprehensive databases compiling species traits are already established in the terrestrial realm, but widely missing in freshwater science. We established a database for European taxa of five aquatic organism groups by compiling information on taxonomy, ecology and distribution based on extensive literature surveys, which were performed by experts for the targeted organism groups. The database includes fishes (654 taxa/21 ecological preferences), macro-invertebrates (8586/40), macrophytes (1083/5), diatoms (8868/36) and phytoplankton (1976/4). It is available online with various options and tools for finding information and has currently over 800 users. The reviewed literature as well as examples given in this paper, highlight the importance of the general availability of knowledge on ecological preferences for various aspects in ecological assessment. Freshwaterecology.info is considered a service for basic research, applied scientists, water managers or other stakeholders. It serves as base for bioassessment and monitoring.