The data management base developed for overview modelling and the modelling process itself have contributed to PLUARG's goal of determining the relative importance of all pollutant sources and in developing plans for pollution abatement from land sources. Overview modelling provides a means of comparing present and future trends in pollutant inputs to the lakes, as well as a methodology for measuring the effectiveness of alternative remedial programs applied to urban nonpoint, rural nonpoint, and municipal point sources. The overview modelling process was used to examine pollutant inputs to southern Lake Huron, Lake Erie, and Lake Ontario.