Urban development influences river systems and associated ecosystems by altering flow mechanics and sediment dynamics. Where river restoration is required, vortex rock weirs (VRWs) provide both physical channel stability and habitat enhancement as a component of natural channel design. Further, rock weirs facilitate fish passage – a common goal in restoring channels impacted by urban development. Field assessments were conducted at a rock weir system to understand fish passage effectiveness. Velocity measurements through a sequence of 10 modified rock weirs were compared to the swimming capabilities of local fish species, and ‘passability’ was identified. Rock weir design was evaluated based on fish passage effectiveness and calibration coefficients were identified to model gap and over-weir flow under different water level conditions. The major contributions from this research inform river restoration initiatives by identifying limitations to in-stream structures, suggesting best practices for rock weir design and monitoring, and influencing fish population management strategies.