There has been a dramatic expansion of dairying in New Zealand in the last two decades. This has been accompanied by a series of environmental issues around water use and water pollution. This thesis looks at the issue of excess nitrogen and phosphorus lost off dairy farms to waterways using a mixed method approach. Qualitative interviews with dairy farmers and GIS based water quality modelling are employed to explore whether the introduction of nutrient benchmarks would achieve sustainable milk production systems. Two Best Practice Dairy Catchments, Waikakahi in South Canterbury and Inchbonnie on the West Coast, were investigated as the study areas. These catchments are part of an established DairyNZ program. Findings show that nutrient benchmarks do have the ability to achieve sustainable milk production systems in the catchments. It presents the implications and recommendations for the benchmarking project.