Phosphorus being one of the essential elements for all forms of life is also a finite resource. The extensive use of Phosphorus in anthropogenic activities has lead to high nutrient load in surface waters causing eutrophication. The Baltic Sea being a semi enclosed water body and a good example of eutrophication has been chosen as model basis. To determine the magnitude of phosphorus use in Riparian States and the total loads to the sea is investigated using a systems analysis approach. In this thesis the phosphorous flows were examined using substance flow analysis of two types of systems: anthropogenic system and a sub basin system. The anthropogenic system presents the flows and stocks of phosphorus within processes with phosphorus utilization within each Riparian country and the total load of phosphorus to the Baltic Sea. The sub basin system models individual sub basins to determine the total input of phosphorus and the resident stocks of phosphorus in sea water and biomass. Based on the sub basin a hypothesis is formulated to determine the fate of phosphorus in the sea and the identify sinks of phosphorus. Hypothesis: The inflow of phosphorus into the Baltic Sea is not coupled with an increase in phosphorus stock but result in a high sedimentation rate. The sub basins represent phosphorus exporters to other neighboring basins. Within the anthropogenic system, agriculture and food market posses the largest flows and stocks of phosphorus. While the largest loads from the anthropogenic systems are from agricultural run off and waste water discharge. Poland is found to have major share in this contribution of phosphorus flows to the Baltic Sea. The sub basin Baltic Proper contains the largest stock of phosphorus among all the other sub basins. The test of the hypothesis hold true and sediments of the Baltic Sea have been recognized as major sinks of phosphorus.