The research reported in this paper is focused on the cost-effectiveness of mitigation strategies to reduce pollution loads and improve water quality in South-east Queensland. To perform the study, scenarios had to be developed about the types of catchment interventions that could be considered, and the resulting changes in water quality indicators that may result. Once these catchment scenarios were modelled, the range of expected outcomes are assessed and costs of mitigation interventions were estimated. Strategies considered include point and non-point source interventions. Predicted reductions in pollution levels were calculated for each action based on the expected population growth. The costs of the interventions included the full investment and annual running costs as well as planned public investment by the state agencies. The results show that the cost-effectiveness of strategies is likely to vary according to whether suspended sediments, nitrogen or phosphorus loads are being targeted.