The article talks about how water pollution is not just about what we can see or smell, but also about hidden sources that are harder to control. These hidden sources, called nonpoint pollution, are responsible for most of the pollution in water. They release things like dirt, nutrients, bacteria, pesticides, and other bad stuff that can make water unhealthy. Scientists are now focusing on these hidden sources because they are a big problem that affects the quality of our water. They are trying to understand where this pollution comes from and how to stop it from getting into our waterbodies. By studying these diffuse sources of pollution, researchers hope to find better ways to keep our water clean and safe for everyone.