This European Standard provides guidance on determining the degree of modification of lake hydromorphological features described in EN 16039. It enables consistent comparisons of hydromorphology between lakes within a country and between different countries in Europe, providing a method for broad based characterization across a wide spectrum of hydromorphological modification. Its primary aim is to assess departure from naturalness for a given type of lake as a result of human pressures, and it suggests suitable sources of information that may contribute to characterizing the degree of modification of hydromorphological features. For wholly artificial lakes or reservoirs formed by damming rivers the aim is to assess the extent to which processes approximate to those in comparable natural water bodies. However, this standard does not replace methods that have been developed within particular countries for local assessment and reporting. Decisions on management for individual lakes require expert local knowledge and vary according to lake type.