Catchment water quality models were recently developed for both Horizons Regional Council (HRC) and Environment Southland (ES) by Dr Tim Cox. The models simulate the generation, transport, and fate of nutrients through dendritic river networks covering the entirety of each region. Calculated nutrient concentrations at key stream locations allow for relative assessments of land management activities and regulatory strategies and comparison to defined nutrient targets or limits. The models were developed using SEL’s Contaminant Allocation and Simulation Model (CASM) software and were calibrated to observed stream concentrations distributed across the stream networks. The HRC models were successfully used to support the proposed Plan Change 2 to the Manawatu-Whanganui One Plan. The ES models will be used by Council staff for ongoing planning decision support, including nutrient limit setting as required by the NPSFM. Model training, and the CASM software generally, will be provided by SEL to ES staff to enable in-house use of the models going forward.