Freshwater habitats are among the most threatened ecosystems worldwide, facing relentless pressure from habitat loss and climate change. As a result, the ability of aquatic species to move between suitable habitat fragments becomes increasingly uncertain. The Island Biogeography Theory suggests that geographic isolation per se could limit biodiversity in fragmented landscapes. Dragon- and damselflies (Odonata) rely on freshwater for reproduction but are highly mobile and easily detectable as adults, which makes them an ideal model system for testing how geographic isolation shapes freshwater invertebrate communities. Making use of openly available and comprehensive geodata and intensive odonate surveys, we quantified the isolation of 99 sites in an Alpine region and tested how isolation influences the diversity and composition of dragon- and damselfly communities. None of three isolation metrics we used affected species richness, community composition or the occurrence of most species, while most of these were affected by elevation, habitat composition and site area. This suggests that dragon- and damselflies can freely disperse within a heterogenous alpine landscape at a regional scale, partly falsifying the Island Biogeography theory in this context. Our results support the common assumption of absent dispersal limitations in ecological models but also calls into question proposals of creating artificial habitats to increase connectivity. Given that habitat composition and site area, had the stronger effect than isolation on all aspects of biodiversity, conservation efforts should prioritize the protection of existing natural habitats and corridors.