Sandy (Alexander) Elliott applies mathematical techniques to address water quality issues, especially predicting the effects of diffuse pollution and its control at catchment scale. His background spans from experimental work on transport process in flumes and on hillslopes, to delivering national-scale catchment modelling software, and from urban areas to the coastal impacts. He has developed and modified several catchment models for water quality, including the national CLUES model, and applied these in a wide range of settings in New Zealand. His current interests include techniques for shifting across spatial and temporal prediction scales and providing practical catchment models suitable for managing water quality within limits. He currently leads NIWA's Eutrophication Risk Assessment programme, and the Our Land and Water Interoperable Models programme.