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The reference conditions are a key concept of the European Water Framework Directive (WFD). This directive holds that the ecological status of a particular water body shall be assessed by quantifying the deviation from the typical reference conditions which refer to a stable state of an ecosystem in the absence of significant human disturbance. This concept is subject to criticism from several authors, all the more since global change will deeply modify the functioning of aquatic ecosystems and their associated biocenosis, whatever the impacts of human activities at local scale. In this paper, an ecologist and a sociologist reconsider the social and scientific construction of the reference conditions concept and associated rules ("one out - all out"). We explain its origin, success and limits, as well as the questions it raises. We point out aspects not considered in this concept and why it challenges the WFD implementation and future management of rivers. [ABSTRACT FROM AUTHOR]