Although 20 years of regulation brought an overall reduction in pollutant loads to the Lake Michigan basin, data indicate that pollutants still negatively affect the chemical, physical, and biological components of the Lake Michigan ecosystem. The rivers and tributaries flowing into Lake Michigan convey the contaminants from their source areas to the lake, and this report attempts to describe the monitoring efforts that have sought to characterize the quality of surface water in the Coastal Nonpoint Pollution Control Plan Area (CNPCPA). For this project, all water-quality data available from several sources were assembled into a database, and analyzed for trends using multiple regression analysis. Of the 1,079 water-quality attributes that were analyzed for trend, 536 (50%) exhibited a statistically significant time trend. Of those, 278 (52%) were positive trends (declining water quality) and 258 (48%) were negative trends (improving water quality). Additional supporting data files (Access database tables) are available for this open-file study.