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Agricultural runoff is a major contaminant source threatening water quality in streams, lakes, and public drinking water reservoirs. Agricultural pollution control practices and programs are traditionally based on the assumption that overland flow is only generated when rainfall intensities exceed soil infiltration capacity. This paper challenges this assumption, noting that overland flow associated with agricultural pollutant transport is often physically consistent with the variable source area hydrology concept, for which overland flow is generated in parts of the landscape where the soil saturates to the surface. Incorporation of variable source area hydrology into watershed management practices reconceptualizes nonpoint source pollution as “variable source pollution,” in which pollution control efforts can be focused on relatively small hydrologically sensitive areas recognizing that the extent of these areas will vary …