This brochure deals with the issue of ecological (minimum) flow. It is a comparative study, not only of how the minimum flow is defined in the legislation of the selected member states, but also how it is implemented and supervised in practice. In a time of progressing climate change and more frequent occurrence of extreme hydrological conditions-- floods and dry periods-- this issue will become more and more important. The brochure focuses on the six selected states of the European Union: the Czech Republic, Germany, Austria, the Netherlands, Finland, and France.