Nonpoint source water pollution comes from large areas or landscapes such as roadways, farms, and urban and suburban communities. Scientists know this type of pollution exists, but it is difficult to identify and control the sources. In this study, scientists were interested in determining how the threat from nonpoint source water pollution varies in watersheds across the United States. Topics: Pollution, Water, Nutrients, Sedimentation, Toxic Chemicals, Water Pollution, Water Quality, Watersheds.