Barriers preventing species from dispersing to a location can have a major influence on how communities assemble, resulting in delayed or poor restoration outcomes due to a lack of dispersing colonists. One key hypothesis describing how dams and weirs affect rivers is that they disrupt longitudinal connectivity, limiting dispersal of biota along rivers. We aimed to determine (a) the patterns of freshwater insect community assembly in new habitats, (b) whether barriers to dispersal affected community assembly within the new habitats, (c) whether dispersal from the newly formed community can alter existing communities in nearby established habitats. This study was centred upon two cobble-bed creeks with weirs, Middle Creek and Diggers Creek, tributaries of the regulated Geehi River and Snowy River respectively. Decommissioning aqueducts on the weirs provided flow to previously dry riverbeds downstream of the tributaries and additional flows to the main-stem regulated rivers. Dispersal via drift was central to community assembly in the newly formed habitat (i.e. tributaries). Even with a significant dispersal constraint (i.e. weirs) reducing the number of colonists from source populations, the recently developed communities rapidly resembled upstream unimpacted communities. In areas with an established community (i.e. regulated rivers), increased dispersal from the tributary did not alter gatherer and scraper densities. Filter feeder densities increased in response to flow from the tributary, due to increased areas of faster-flowing habitat and oviposition substrates, and greater food resources, not higher dispersal rates. Our study indicated that in newly created stream habitat, there were no long lasting effects of reduced dispersal on freshwater invertebrate community assembly. Responses to tributary flows in established communities were limited and related to alleviation of environmental constraints for particular species. Increasing rates of dispersal did not substantially alter existing communities and suggests priority effects may limit colonisation of some species in regulated rivers.