Lake hydromorphology assessment in Europe: Where are we 20 years after the adoption of the Water Framework Directive?

International audience; The characterization of lake hydromorphology is crucial to understand the dynamics of biodiversity. In Europe, it isalso a regulatory requirement of the Water Framework Directive. However, according to the literature, few methodsinclude this characterization. The aim of this study is to review the state of the art of the methods currently used orunder development in European countries to assess lake hydromorphological status for the implementation of theWFD. Our analysis is based on responses to a questionnaire distributed to national experts on hydromorphologyof the 28 countries implementing the WFD. Our results highlighted significant progress in the assessment ofhydromorphological features and processes. Water level regime, through the range of water flow or existing watermanagement, and structure of the shore zone through macrophytes and substrate characteristics or measurement oflateral connectivity, are the most frequently assessed features. Stratification, surface/groundwater connection andplanform pattern are the lake features most frequently omitted from the methods. However, in most of the countries,the development of methods was still in progress to meet the WFD requirement. Definition of reference condition is acentral component of all WFD compliant assessment tools but this is a challenge particularly in the assessment ofhydromorphological alteration of reservoirs. Similarly, demonstrating strong links between hydromorphological indicatorsand biological quality elements remains a challenge with many knowledge gaps still evident. These results highlight the need for rapid collection of new environmental data and the need for conceptual and applied research to make methodological progress in assessing lake hydromorphology and ensuring habitat quality.