Spatial dynamics and local environmental processes shape ecological communities and affect diversity in dendritic riverine networks. Understanding the contributions of individual and interacting parameters on diversity and community composition is a contentious topic. Recent theoretical work suggests that diversity in dendritic networks is to a large extent explained by dispersal and network connectivity. Empirical studies identified similar diversity patterns depending on network position but also found that contribution of relevant processes differed depending on scale. In this study I explored α-, true β-, and functional diversity within aquatic invertebrate communities and identified variables that explained diversity patterns at two levels of taxonomic resolution (species/complex-level and family-level). The studied area encompasses the dendritic network of the pre-alpine river Thur drainage basin that spans over seven Strahler orders. Macroinvertebrate samples and chemico-physical parameters were taken at 60 sites selected to represent the Thur’s inherent network structure, from 2^nd-order headwaters to 7^th-order rivers. Using regression analysis, linear, and general linear models, I related diversity patterns to network connectivity, network distance, and a set of local environmental variables. On both levels of taxonomic resolution, I found that local diversity showed a unimodal distribution that peaked in mid-sized stream reaches. Low α-diversity contrasted with high true β-diversity in headwaters. Local diversity was best explained by distance from outlet and by a set of chemical variables that indicate anthropogenic impact on water quality. Using model selection, it was not possible to reduce the explanatory variables and interactions to a straightforward set that best explained true β-diversity. My results highlight the importance of local factors such as chemical content of stream water and spatial position within the river network on local macroinvertebrate diversity. Furthermore, constraints of partially treated waste water on the composition and structure of aquatic invertebrate communities were indicated.