Stream macroinvertebrate communities are strongly altered by catchment conversion to agricultural land-uses. Are these changes similar across regions with different levels of gamma diversity? We surveyed macroinvertebrate communities in 18 species-rich streams across Tasmania over a gradient of agricultural land use and contrasted these results to a similar survey of 16 streams in Western Australia, which have naturally depauperate macroinvertebrate gamma diversity. We found that the community structure and composition in forested streams was more spatially variable than in agricultural streams in both regions. Agricultural land-uses seem to have homogenized the fauna beyond a threshold of catchment conversion. Despite having higher gamma diversity, this threshold was observed in both Western Australian and Tasmanian streams, implying that agricultural stressors influence community structure and composition to make the invertebrate fauna of stream reaches more homogeneous regardless of the original community composition or its inherent level of diversity.