We studied the relationships between structural and functional diversity within and among macrophyte communities of softwater lakes. Diversity was assessed based on Simpson’s diversity index (SD), species richness (S), Rao’s functional diversity (FDQ) and shared plant traits along a gradient of pH. A total of 10,800 cover-plant samples (area=0.1 m2) were analysed, collected from 241 sections of the bottom (with a depth resolution of 1.0 m) of 38 lakes in Poland. We identified 59 species of macrophytes and recognized four communities. Along a gradient of increasing pH we found i) an increase of species richness; ii) a uniformity of abundance in communities; and iii) an increase in the quantitative contribution of life history traits such as perennials, submerged anchoring, leaf placement along an orthotropic shoot and generative reproduction. On the other hand, there was a decrease in unanchored and evergreen perennials. In our study, we found that the variety of these traits within communities is greater than that between them. Within lakes, structural diversity was low, whereas it was high between lakes. Functional diversity exhibited an opposite pattern: it was high at lake scale, and low between lakes. A combination of partitioning diversity and utilizing environmental variables significantly improves the prediction of community structure and the conservation of lakes.