Water quality standards (QS) and river monitoring are widely accepted as preventive management strategies for the preservation of watercourses and at the same time they are criticized for imposing universal threshold values, leading to regulatory rather than voluntary action. Based on the example of nitrate, the article explains how QS applications are the result of national or regional negotiations, with no direct link to the scientific foundations underlying the development of these tools. These conflicting perceptions and how these tools are actually used are illustrated by the situation in Brittany. Here, the monitoring network and actions to prevent increasing nitrate concentrations in rivers form part of regional programs set up jointly by all the main stakeholders. However, while QS can act as an alarm signal, their effectiveness depends on local political support, which depends on the extent to which river quality is recognized as a key factor in regional development.