Urbanization is the second-highest global cause of habitat loss and lotic ecosystems are especially vulnerable to the adverse effects of urbanization because of their close connectivity with surrounding terrestrial ecosystems. There is, however, a knowledge gap in how the taxa and functions of benthic macroinvertebrate assemblages respond to a gradient of urban land use and where their tipping points are along this gradient. Thus, we aimed to quantify how catchment urbanization influenced benthic macroinvertebrate functions and taxa. We found that most significant change points of both taxonomic and functional composition occurred at < 20% of catchment urbanization. These results show that even small amounts of catchment urbanization can alter both the taxonomic and functional structure of macroinvertebrate assemblages. Thus, maintaining lotic ecosystem biodiversity requires excluding or mitigating catchment urbanization. Although this is a difficult proposition because of historical linkages between urbanization and streams, the ecosystem services that urban streams and their biota provide are essential to the long-term sustainability of urban centers and their populations.