Recent opinion surveys point to water pollution, primarily from pastoral agriculture, as the largest environmental issue in New Zealand. With a prognosis for increased land use intensification, further water quality degradation seems highly likely. This paper outlines five major aspects of the diffuse pollution issue: 1. Characterisation of diffuse pollution and the shift from point to diffuse sources. The ‘universal’ diffuse pollutants: nutrients, fine sediments, and pathogens, all of which are mobilised by livestock, predominate in New Zealand waters. There has been a shift over the last 40 years from point sources to diffuse sources as the major contributors of pollution, with point sources now accounting for only 3.2% of the total nitrogen, and 1.8% of the total phosphorus fluxes to the sea. 2. Pathways of diffuse pollutants. Diffuse pollutants move into waters through: overland runoff; direct access to waters by livestock; and leaching to groundwater (often with associated legacy issues reflecting groundwater residence times). These pathways are discussed illustrating the importance of understanding processes – particularly for targeting Beneficial Management Practices (BMPs). 3. Attenuation of diffuse pollutants through interception mechanisms and BMPs adjacent to, and in, streams. Attenuation is discussed for riparian zones, and in-stream processing. 4. Modelling of diffuse pollution has been done in New Zealand through mechanistic, stochastic and statistical approaches, and management-accessible models are described. 5. Managing diffuse pollution needs to recognise that catchments are the most appropriate spatial management unit. Managing diffuse nutrient loads has recently been initiated in New Zealand through regulation by setting load limits (nutrient caps) on catchments, and through identified nutrient concentration targets.