The Water Framework Directive (WFD) has provided the means of standardizing the way surface water bodies are monitored throughout the European Union (EU), using a common evaluation measure, the percentage of surface water bodies at good status, based largely on the structure and functioning of aquatic ecosystems. However, the evaluation of good status is based on the way the WFD is implemented, which differs in each country. In this article, we analyze how the WFD is implemented in France, how the water agencies divide up the water bodies, the areas covered by their monitoring networks, and the modalities of obtaining data to provide the EU with the percentage of water bodies at good status. This analysis reveals that it is this hyperindicator itself that is at stake, obtained by successively aggregating values measured in time and space, from the monitoring station to the River Basin District (RBD), reducing vast amounts of information to a single measure per RBD, while long-term monitoring of the major European rivers and their sedimentary budgets, which show improvements in certain quality aspects, are largely overlooked by the WFD. When drawing up the indicator, the agencies identify certain biases but not others. This raises the question of its use and relevance for managers and politicians, at both national and European level.