Pollution loading from recreational boating has been gleaned from seasonal boat count data, published results of pollutant releases from marine engines, and boat type and size distributions from marine association data. These loading functions have then been used in the single-basin MSB model of pollution-flushing, a systems-dynamic model written in Stella (Stella is a product of ISEE Systems, Inc., formerly High Performance Systems of Hanover, New Hampshire, USA), which has been validated in tank tests and in a specific application to Great Salt Pond on Block Island. The results of the present study allow the concentration of various aqueous pollutants associated with the propulsion component of recreational boating to be computed in well-mixed tidal embayments.