European shallow lakes; epiphyton; Bacillariophyta; bioindication; eutrophication; total phosphorus Diatom-based assays have been successfully associated worldwide with the trophic status of lakes. Several studies have demonstrated a correlation between epiphytic diatoms and nutrient load in shallow lakes and wetlands. We examine the relative importance of environmental factors in explaining the structure of epiphytic diatom communities in a set of Western European shallow lakes. The effects of lake physical/chemical, morphometric and geographical variables on diatom assemblages were tested using distance-based, canonical correspondence and regression analyses. Our results show that epiphytic diatom communities respond, mainly to physical/chemical variables, overriding the effects of lake depth, size and location. The clustering of studied systems based along a total phosphorus concentration gradient concurs with previous classification of diatom taxa and nutrient state. Assessment of epiphytic diatoms provided a potential method for shallow lake classification.