This paper is concerned with the development of a predictive tool to determine the heat diffusion profile for turbulent discharge of heated water into a body of still receiving water. The process makes use of a thermal imaging camera to measure the discharge plume from a range of sites in order to observe the actual discharge and then to provide a mathematical model that will allow British Waterways to satisfy the Environmental Agency regulations. In addition the sites are replicated in a laboratory environment with a scale model tank that allows the mixing zones to be measured under variable conditions. In this case the heated water is dyed to provide a visual plume in addition to the thermal image. The plume and mixing zones are then predicted using appropriate software such as Matlab, the model being optimised to reflect the real measured discharges.