Describe an example of a non-point source of water pollution.

Agricultural runoff from fields during rainfall is a quintessential example of a non-point source of water pollution because it originates from widespread and diffuse areas rather than a single, identifiable source. Non-point source pollution refers to contaminants that are washed off across various surfaces, making it difficult to pinpoint the exact origin of the pollutants. In this scenario, rainwater can pick up fertilizers, pesticides, sediments, and other harmful substances from fields and transport them into nearby water bodies.

This kind of pollution is particularly problematic because it can vary in intensity and composition depending on factors like weather conditions, land use, and farming practices, thereby complicating management and mitigation efforts. The cumulative effect of such runoff across a landscape can significantly impact water quality in rivers, lakes, and streams, leading to issues such as algal blooms and decreased aquatic life.

In contrast, the other examples provided represent point sources of pollution, where contaminants are discharged from specific locations, making them more identifiable and often subject to regulatory controls.