Evidence is emerging that global supplies of rock phosphate used for production of phosphorus (P) fertilizers are declining. The term peak phosphorus has been applied to the situation that phosphorus, the first non-renewable, non-substitutable life-supporting element, will become scarce in the foreseeable future. As a result, management of phosphorus on the land and the prevention of nutrient pollution in aquatic ecosystems are aligned by the common goal of keeping phosphorus on the land for crops. The objective of the study was to investigate the confluence of intensive management of phosphorus in agriculture with the goals of securing food productivity and water pollution prevention as symbolized by Lake Winnipeg, visibly the most eutrophic Great Lake in the world. The method was an action research approach designed to disseminate and gather information on existing and future challenges related to P management and social process of change. Based upon review of science, analysis of the basin and dialogue with 40 stakeholders, action recommendations for best management practices, P recycling and stewardship were formulated. The results demonstrate the urgency and importance of establishing an integrated watershed management approach including all aspects of Lake Winnipeg-related water security, phosphorus recycling, traditional knowledge and governance.