This study from Vietnam looks at the pollution problem caused by fish farming in the Mekong Delta (MD) and assesses a number of treatment options that could bring this pollution down to acceptable levels. The study is the work of a research team led by Ms Vo Thi Lang, from Cantho University in Vietnam. It finds that a trickling-filter system would be the most cost-effective response to this challenge. However such a system would cost farmers more than they currently pay to discharge their polluting wastewater. The study therefore suggests a number of policy options that would encourage fish farmers to reduce the amount of pollution they discharge and help them to meet the necessary clean up costs.