The monitoring of point sources by the Environmental Protection Agency (EPA), the states, and the tribes has documented and helped reduce the levels of chemical stressors affecting our ecosystems. With the controls on point sources reducing chemical contamination, new environmental challenges associated with nonpoint sources have emerged. To adequately deal with these new problems, EPA's Office of Research and Development recognized the need to develop an overall under standing of the condition of our ecological resources, the trends in their condition, and the stressors affecting these...

The Environmental Monitoring and Assessment Program was created by EPA to develop the capability for tracking the changing conditions of our natural resources and to give environmental policy the advantages ofa sound scientific understanding of trends. Former EPA Administrators recognized early that contemporary monitoring programs could not even quantify simple unknowns like the number of lakes suffering from acid rain, let along determine if national control policies were benefiting these lakes. Today, adding to acidification impacts are truly complex problems such as determining the...