The case studied is the Gulf of Finland, which forms part of the Baltic Sea. They present a dynamic model that integrates land loads of nitrogen and phosphorus, cost of nutrient abatement measures in agriculture, nutrient dynamics in the sea basins adjoining the Finnish coast, exogenous risk of oil spills, and recreational value of the sea, which faces environmental damage of uncertain magnitude and duration. Monte Carlo simulation is applied to evaluate the profitability of nutrient abatement measures carried out unilaterally by Finland or as a joint effort by Estonia, Finland and Russia.