Urban growth in the vicinity of Hadspen and Carrick in northern Tasmania is projected to increase significantly from recent rezoning of land east and south-east of Hadspen. The projected growth will increase sewage inflows to the Carrick Sewage Treatment Plant (STP), requiring an upgrade to the existing plant infrastructure. The volume of wastewater to be discharged to the Meander River is also expected to double. This study aimed to assess the potential impacts of future Carrick STP wastewater discharges on environmental values in the Meander River receiving environment. We developed a simple model to simulate water quality conditions (i.e. total nitrogen, total phosphorus, ammonia, nitrate, suspended solids, electrical conductivity and enterococci) in the Meander River upstream and downstream of the Carrick STP outfall. The model ran on a daily time step, calibrated on current conditions and modified for future scenarios. We evaluated the risk posed to environmental values based on the percentage of time water quality objectives (WQOs) were achieved in the Meander River under different seasonal and flow conditions. Risk-based emission limits were recommended for the Carrick STP upgrade based on this analysis and the contribution of the Carrick STP wastewater to catchment nutrient loads. The findings of this study were incorporated in the Development Proposal and Environmental Management Plan for the Carrick STP upgrade and allow future planning to go-ahead with confidence.