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...